WO2020095660A1 - Glass product which has three-dimensional shape and method for manufacturing same, and chemically strengthened glass product and method for manufacturing same - Google Patents

Abstract

Provided is a glass product which has a shape other than a flat plate shape and has a glass composition comprising, represented in mass% on an oxide basis, 60 to 70% of SiO2, 6 to 18% of Al2O3, 2 to 8% of Li2O, 8 to 20% of Na2O, 0 to 1% of K2O, 0 to 3% of MgO, 1 to 6% of CaO, and 0.01 to 0.2% of Fe2O3. This glass composition is suited for being made into a three-dimensional shape using a mold press method and for being strengthened by a chemical strengthening process.

Description

Glass article having three-dimensional shape and method for producing the same, chemically strengthened glass article and method for producing the same

The present invention relates to a glass article having a three-dimensional shape and a chemically strengthened glass article, which contains an alkali aluminosilicate glass containing lithium. In addition, in this specification, a "three-dimensional shape" means a shape other than a flat plate.

In recent years, mobile terminals equipped with a touch panel have become widespread, and it is common to equip the surface of the display with a cover glass to protect the display. As the cover glass, for example, a plate-shaped alkali aluminosilicate glass having a thickness of about 0.3 mm to 1 mm chemically strengthened is used.

More recently, with the development of displays having a three-dimensional shape such as a curved shape, a cover glass having a three-dimensional shape is expected. Also, in order to improve the radio wave transmission / reception of the built-in antenna of the mobile terminal, a chemically strengthened glass housing having a three-dimensional shape is used in place of the metal housing to improve the radio wave transmission / reception of the built-in antenna of the mobile terminal. It is also expected to do. On the other hand, there has been proposed a cover glass that is processed from a flat plate shape into a three-dimensional shape by thermal processing and is chemically strengthened (Patent Documents 1 to 4).

As a three-dimensional shape, for example, Patent Document 1 discloses "curved surface shape, uneven shape, corrugated shape, stepped shape, etc." Further, in Patent Document 2, a flat plate glass is bent as a "dish shape" and is raised at a predetermined angle with respect to the main surface thereof, which should be a plate shape, a bat (tray) shape, or a box shape (Fig. 1). , FIG. 2) is illustrated. Further, Patent Documents 4 and 5 exemplify those molded into a uniform curved surface.

As a method of forming a flat glass into a three-dimensional shape, a self-weight forming method of heating and bending the flat glass, a vacuum forming method (sagging or suction method), etc. are known (for example, Patent Documents 5 and 6).

When forming a three-dimensionally shaped glass article (see FIGS. 1 and 2 of Patent Document 2) having a bent portion that is locally bent instead of a uniform curved surface, particularly, the shape and thickness distribution thereof are precisely controlled. When it is required to do so, the mold pressing method is most suitable (Non-Patent Document 1). This is a method which is originally widely used for press molding of aspherical lenses, but flat glass can also be used as a preform. Compared with other thermal processing methods, the mold pressing method has a high degree of freedom in designing the shape of a glass article having a three-dimensional shape, that the shape can be precisely controlled and formed, and the surface may be different depending on the condition of the mold surface. It has advantages such as obtaining a glass article having a smooth three-dimensional shape.

There are the following problems in obtaining a glass article having a three-dimensional shape by the above-mentioned mold pressing method using a flat glass composed of the glass composition disclosed in Patent Documents 1 to 4 as a preform.

Patent Document 1 discloses a glass article having an alkali aluminoborosilicate glass composition. However, since the glass composition disclosed in Patent Document 1 has a high characteristic temperature such as a softening point, a mold pressing method using a flat glass as a preform at a relatively low processing temperature (for example, around 600 ° C.) is applied. Not suitable to do.

Also, Patent Documents 2 to 5 do not disclose a glass composition suitable for applying the mold pressing method in which a flat glass is used as a preform at the processing temperature.

It should be noted that since the degree of improvement in the strength of a glass article due to chemical strengthening is greatly influenced by the glass composition near the surface of the glass article, it is usually the strength improvement of the glass article that the glass composition near the surface of the glass article changes due to thermal processing. Work against you. From that point as well, thermal processing at high temperature is not preferable.

For this problem, a method of subjecting flat glass to chemical strengthening and then heat processing is conceivable. In that case, stress relaxation occurs due to diffusion of ions introduced by ion exchange, and the compressive stress applied to the surface of the glass article is reduced, which makes it difficult to apply the isothermal pressing method.

JP, 2010-168233, A Japanese Patent Publication No. 2015-527277 Japanese Patent Publication No. 2015-527970 Japanese Patent Publication No. 2017-506616 International Publication No. 2016/125713 Japanese Patent Publication No. 2011-526874

The problem to be solved by the present invention is to impart a three-dimensional shape using a mold pressing method, and further to strengthen it by a chemical strengthening treatment, having a glass composition suitable for the three-dimensional shape. To provide a glass article provided. Further, the problem to be solved by the present invention is to provide a glass article having such a glass composition, having a three-dimensional shape, and having a high strength by a chemical strengthening treatment.

The present invention is
Has a three-dimensional shape, that is, a shape other than a flat plate,
Displayed in mass% based on oxide,
SiO ₂ 60% or more, 70% or less,
Al ₂ O ₃ 6% or more, 18% or less,
Li ₂ O 2% or more, 8% or less,
Na ₂ O 8% or more, 20% or less,
K ₂ O 0% or more, 1% or less,
MgO 0% or more, 3% or less,
CaO 1% or more, 6% or less,
Provided is a glass article containing 0.01% or more and 0.2% or less of Fe ₂ O ₃ .

Further, the present invention is
From the molten glass raw material, represented by mass% on an oxide basis, to form a flat glass having a glass composition containing each of the above components in the above content ratio,
Molding the flat glass into a glass article having a shape other than a flat plate by a mold pressing method, and a method for producing a glass article.

Further, the present invention is
Has a shape other than a flat plate,
Has a compressive stress layer on the surface,
At least the portion other than the compressive stress layer is displayed by mass% based on oxide,
Provided is a chemically strengthened glass article containing the above components in the above content rates.

Further, the present invention is
From the molten glass raw material, represented by mass% on an oxide basis, to form a flat glass having a glass composition containing each of the above components in the above content ratio,
Forming the flat glass into a glass article having a shape other than a flat plate by a mold pressing method,
A method for producing a chemically strengthened glass article, comprising: chemically strengthening the glass article.

Further, the present invention is
Provided is a mobile terminal provided with the glass article according to the present invention.

Further, the present invention is
Provided is a vehicle-mounted display device including a glass article according to the present invention.

According to the present invention, a glass having a glass composition suitable for imparting a three-dimensional shape by using a mold pressing method and further increasing the strength by a chemical strengthening treatment and having a three-dimensional shape imparted thereto. Articles are provided. Further, according to the present invention, there is provided a glass article having such a glass composition, imparted with a three-dimensional shape, and strengthened by a chemical strengthening treatment.

The glass composition specified by the present invention enables molding by a mold pressing method at a relatively low temperature. The mold press method at a relatively low temperature suppresses problems that may occur with the mold press method such as reduction of transmittance of glass articles due to devitrification, roughening of the surface of glass articles, wear of mold used for molding, etc. It is advantageous in doing so. Further, the glass composition specified by the present invention enables chemical strengthening treatment after molding, and is suitable for realizing a high-strength glass article having a three-dimensional shape. In the present invention as well, the molding temperature by the mold pressing method may be higher if necessary. Molding at a higher temperature is preferably applied when the flat glass is molded into a specific shape, for example, a shape in which the side plate portion is thicker than the bottom plate portion. The glass composition specified by the present invention can provide the advantage that molding into glass articles of such different thicknesses can also be carried out at lower temperatures.

The top view which shows an example of the shape of the glass article which has a three-dimensional shape. II-II sectional view of FIG. III-III sectional view of FIG. The top view which shows another example of the shape of the glass article which has a three-dimensional shape. VV sectional view of FIG. VI-VI sectional view of FIG. The top view which shows another example of the shape of the glass article which has a three-dimensional shape. VIII-VIII sectional view of FIG. IX-IX sectional view of FIG. The top view which shows another example of the shape of the glass article which has a three-dimensional shape. The figure which shows the temperature-viscosity curve of the glass composition of Examples 1-3. The figure which shows the compressive stress distribution in the depth direction of the chemically strengthened glass article which consists of the glass composition of Example 1. The figure which expanded a part of FIG. The figure which shows the concentration distribution of the depth direction of sodium ion in the surface vicinity of the chemically strengthened glass article which consists of the glass composition of Example 1.

Hereinafter, the present invention will be described with reference to the drawings as appropriate, but the following description does not limit the present invention to a particular mode.

[Three-dimensional shape of glass article]
The glass article has a shape other than a flat plate, that is, a three-dimensional shape. The three-dimensional shape is, for example, a shape including a bottom plate portion, a bent portion, and a side plate portion, and the side plate portion is connected to the peripheral edge of the bottom plate portion via the bent portion.

1 to 3 show examples of the above shapes. The glass article 10 has a shape in which the side plate portion 2 is connected to the entire peripheral edge of the bottom plate portion 1 via the bent portion 3. The bottom plate portion 1 has a substantially quadrangular shape in a plan view, to be precise, a rectangular shape with rounded corners. The bottom plate portion 1 is a flat plate, and the main surface 1f thereof is a flat surface. The side plate portion 2 rises from the bent portion 3 to the same height as viewed from the main surface 1f of the bottom plate portion 1. The side plate portion 2 extends in a direction away from the main surface 1f that is the bottom surface of the bottom plate portion 1. Both the side plate portion 2 and the bent portion 3 have curved surfaces (see FIGS. 2 and 3), and the surface of the bent portion 3 has a larger curvature than the surface of the side plate portion 2.

4 to 6 show another example of the above shape. The bottom plate portion 1 of the glass article 20 has a peripheral edge to which the side plate portion 2 is connected via the bent portion 3 and a peripheral edge to which the side plate portion 2 is not connected. The bottom plate portion 1 has a substantially quadrangular shape in plan view, and more specifically, a rectangular shape. The side plate portion 2 rises from the peripheral edge of the bottom plate portion 1 corresponding to a pair of opposite sides of the rectangle facing each other through the bent portion 3, and the end surface of the bottom plate portion 1 is exposed at the peripheral edge corresponding to the other opposite side of the bottom plate portion 1. ing.

7 to 9 show another example of the above shape. Also in the glass article 30, the bottom plate portion 1 has a peripheral edge to which the side plate portion 2 is connected via the bent portion 3 and a peripheral edge to which the side plate portion 2 is not connected. However, unlike the glass article 20, in the glass article 30, the side plate portion 2 rises through the bent portion 3 from the peripheral edge corresponding to the long side of the main surface of the bottom plate portion 1 instead of the short side. Further, unlike the glass articles 10 and 20, the bottom plate portion 1 of the glass article 30 is a curved plate whose main surface 1c is a curved surface (see FIG. 9).

The shapes shown in FIGS. 1 to 9 are dish-shaped, bat (tray) -shaped and the like. Further, if the side plate portion 2 is extended further from the shape shown in FIGS. 1 to 3, it can be called a box shape. Thus, the glass article may have a shape corresponding to at least one selected from a dish shape, a bat shape, and a box shape. However, the shape of the glass article is not limited to the examples shown in FIGS. For example, the bottom plate portion 1 is not limited to a quadrangle in a plan view, and may have a circular shape, an elliptical shape, or the like. The side plate portion 2 may be a flat plate or may rise in a direction orthogonal to the main surface of the bottom plate portion 1. The side plate portion 2 may be provided with notches, holes or the like for connecting a connector or the like to the mobile terminal. A hole or the like may be formed in the bottom plate portion 1. The shape of the glass article is not limited to the shape including the bottom plate portion, the bent portion, and the side plate portion. For example, the glass article 40 shown in FIG. 10 does not have a portion that can be regarded as a bent portion when the side plate portion 2 having a constant curvature is directly connected to the peripheral edge of the bottom plate portion 1 that is a flat plate in a cross-sectional view.

A glass article typically has a shape that can be applied by deforming a plate-shaped glass article having a pair of main surfaces that are flat, that is, flat glass, by a mold pressing method. The glass article preferably has a bottom plate portion 1 as a main portion thereof, specifically, a portion occupying a majority of the whole on a mass basis, and the bottom plate portion 1 preferably has a flat plate shape or a curved surface shape. A preferable curved surface shape of the bottom plate portion 1 is a smooth curved surface having a minimum radius of curvature of 5 cm or more. The shape of the bottom plate portion, which is a flat plate or a curved plate having a small curvature, is suitable for use as, for example, a front surface portion arranged on the front surface of a display such as a mobile terminal or a bottom portion of a glass housing of the mobile terminal.

The thickness t1 of the bottom plate portion 1 is, for example, 0.3 mm or more and 2 mm or less, and particularly 0.3 mm or more and 1 mm or less. This thickness is suitable for use as a cover glass or glass housing for mobile terminals. However, when the bottom plate portion 1 is used in a display device other than that for a mobile terminal, it may have a thickness suitable for it.

The thickness t2 of the side plate portion 2 may also be, for example, 0.3 mm or more and 2 mm or less, particularly 0.5 mm or more and 2 mm or less. Further, the thickness t2 may be substantially the same as the thickness t1 of the bottom plate portion 1. In the glass article, the thickness may be substantially the same over the entire area of the bottom plate portion 1 and the side plate portion 2. In the present specification, "substantially the same thickness" means that the difference in thickness is 0.1 mm or less, and further 0.05 mm or less.

However, not limited to this, the thickness t2 is not substantially the same as the thickness t1 and may be larger than the thickness t1. In this case, the difference (t2-t1) may be, for example, 0.3 mm or more, and particularly 0.4 to 1 mm. By making the side plate portion 2 thicker than the bottom plate portion 1, while suppressing an increase in the weight of the entire glass article, 1) the weight of the bottom plate portion 1 itself and the pressure applied to the bottom plate portion 1, for example, the pressure applied to the display by a finger or the like are prevented. The strength of the side plate 2 can be easily maintained, and 2) the strength of the side plate 2 can be easily maintained even if the side plate 2 is provided with a notch or a hole. In order to sufficiently obtain such an effect, the thickness t2 may be twice or more the thickness t1.

Note that the thickness t2 of the side plate portion 2 may be locally thicker than the thickness t1 of the bottom plate portion 1. For example, in order to obtain the effect of 1), only one or two or more columnar portions extending from the connecting portion with the bent portion 3 and reaching the end surface of the side plate portion 2 are locally thickened so that the side plate portion 2 has a supporting portion. Should be provided. Further, for example, in order to obtain the effect of 2), it is preferable to locally thicken the portion where the notch is provided. In these cases, it is preferable that the difference (t2p-t1) between the thickness t2p and the thickness t1 of the locally thickened portion is within the range described above for the difference (t2-t1).

As will be described later, if the conditions of the mold pressing method are appropriately selected, a glass article in which the thickness of the side plate portion 2 is substantially the same as the thickness of the bottom plate portion 1 is produced from a flat glass having substantially the same thickness. It is also possible to form a glass article in which the side plate portion 2 is thicker than the bottom plate portion 1 from the above flat glass.

The surface of the glass article can have high smoothness even after applying the mold pressing method and the chemical strengthening treatment. The arithmetic average roughness Ra of the surface is, for example, 1 nm or less, and further 0.8 nm or less. Further, the glass article may have a high light transmittance even after applying the mold pressing method and the chemical strengthening treatment, at least in the bottom plate portion 1. The change in light transmittance compared with the flat glass that is the preform before applying the mold pressing method and the chemical strengthening treatment is within 2%, further within 1%, as expressed by the average transmittance in the wavelength range of 400 to 1200 nm. Is.

[Glass composition]
The glass composition of the glass article is an alkali aluminosilicate glass containing lithium oxide (Li ₂ O). Hereinafter,% indications indicating the components of the glass composition mean mass% on the oxide basis. Further, in the present specification, "substantially free from" means that the content of the component is 0.05% or less, preferably 0.01% or less. In industrial mass production of glass articles, it may be unavoidable to mix impurities. “Substantially” means that unavoidable mixing of a trace amount of impurities is allowed.

The preferable range of the content of each component (SiO ₂ , Al ₂ O ₃ , Li ₂ O, Na ₂ O, K ₂ O, MgO, CaO, Fe ₂ O ₃ ) constituting the glass composition of the glass article is described above. It is as follows.

The glass article may further contain, for example, the following components as a coloring agent and a clarifying agent.
TiO ₂ 0% or more, 1% or less,
SO ₃ 0% or more, 1% or less,
SnO 0% or more, 1% or less,
CeO ₂ 0% or more, 1% or less,
As ₂ O ₃ 0% or more, 1% or less,
Sb ₂ O ₃ 0% or more and 1% or less However, it is desirable that As ₂ O ₃ and Sb ₂ O ₃ are not substantially contained. Other optional components will be described later.

Below, we will explain in more detail the preferred content of each component.

(SiO ₂ )
If the content of SiO ₂ is too low, the chemical durability such as water resistance of glass and the heat resistance decrease. On the other hand, if the content of SiO ₂ is too high, the viscosity of the glass composition at high temperature becomes high, which makes melting and molding difficult. Therefore, the SiO ₂ content is in the range of 60 to 70%, preferably 60 to 68%, more preferably 62 to 66%, and most preferably 64 to 66%.

(Al ₂ O ₃ )
Al ₂ O ₃ improves chemical durability such as water resistance and further facilitates the movement of alkali metal ions in the glass to increase the surface compressive stress after chemical strengthening and to increase the stress layer depth. It is an ingredient for deepening. If the proportion is less than 6%, the effect is insufficient. On the other hand, if it exceeds 18%, the viscosity of the glass melt becomes high, and it becomes difficult to melt and mold, and the expansion coefficient becomes too small. Therefore, the content of Al ₂ O ₃ is in the range of 6 to 18%, preferably 10 to 18%, more preferably 14 to 17%.

(Li ₂ O)
Li ₂ O is a component for performing ion exchange and also a component for enhancing solubility. If the proportion is less than 2%, sufficient surface compressive stress after ion exchange cannot be obtained, and the solubility is poor. On the other hand, if it exceeds 8%, the water resistance after ion exchange is deteriorated, and the liquidus temperature rises, making molding difficult. Therefore, the Li ₂ O content is in the range of 2 to 8%, preferably 2 to 6.1%, more preferably 2.6 to 6%, and further preferably 3 to 5%.

(Na ₂ O)
Na ₂ O is a component that enhances the solubility. If the proportion is less than 8%, the effect is insufficient. On the other hand, if it exceeds 20%, the water resistance after ion exchange is deteriorated. Therefore, the content of Na ₂ O is in the range of 8 to 20%, preferably 10 to 16%, more preferably 10 to 14%, and most preferably 11 to 13%.

(K ₂ O)
K ₂ O is a component that enhances solubility, but it is not an essential component because the surface compressive stress after ion exchange may decrease. Therefore, the content of K ₂ O is in the range of 0 to 2%, preferably 0 to 1%, more preferably 0 to 0.5%, most preferably 0.3 to 0.5%.

(MgO)
MgO is a component that enhances the solubility, but if it exceeds 3%, the liquidus temperature rises, and molding becomes difficult. Therefore, the MgO content is in the range of 0 to 3%, preferably 0 to 2%, more preferably 0.5 to 2%, and most preferably 0.5 to 1.5%.

(CaO)
CaO is a component that enhances the solubility and an essential component for adjusting the ion exchange rate. If the proportion is less than 1%, the effect is not sufficient. On the other hand, if it exceeds 6%, the liquidus temperature rises and molding becomes difficult. Therefore, the CaO content is in the range of 1 to 6%, preferably 1 to 4%, and most preferably 2 to 4%.

(Fe ₂ O ₃ )
Usually, Fe is present in the glass in the state of Fe ²⁺ or Fe ³⁺ and acts as a colorant. Fe ³⁺ is a component that enhances the ultraviolet absorbing performance of glass, and Fe ²⁺ is a component that enhances the heat ray absorbing performance. When the glass article is used as a cover glass for a display, it is required that the coloring is inconspicuous. Therefore, the Fe content is preferably low. However, Fe is often inevitably mixed with industrial raw materials. Therefore, when used as a cover glass for a display, the content of iron oxide converted to Fe ₂ O ₃ is 0.2% or less, preferably 0.15% or less, more preferably 0.1% or less, It is preferably 0.05% or less, but may not be completely excluded, and may be 0.01% or more.

On the other hand, when a chemically strengthened glass article having a three-dimensional shape is used as the glass housing, the iron oxide content converted to Fe ₂ O ₃ is 0.1% or more for the purpose of coloring, and more preferably It may be suitable to be 0.5% or more.

(Other ingredients)
SrO and BaO are components that enhance the solubility and are effective in lowering the liquidus temperature. However, as the density of glass increases, the cost of raw materials increases. The contents of SrO and BaO are each in the range of 0 to 1%, preferably 0 to 0.5%, more preferably 0 to 0.1%. Most preferably, the glass article is substantially free of SrO and BaO.

B ₂ O ₃ is a component that lowers the viscosity of the glass composition and improves the solubility. However, if the B ₂ O ₃ content is too high, the glass composition is likely to undergo phase separation, and the water resistance of the glass composition is reduced. Further, the compound formed by B ₂ O ₃ and the alkali metal oxide may volatilize and damage the refractory in the glass melting chamber. Further, the inclusion of B ₂ O ₃ makes the depth of the compressive stress layer in chemical strengthening shallow. Therefore, the B ₂ O ₃ content is suitably 0.5% or less, preferably 0.1% or less. Most preferably, the glass article is substantially free of B ₂ O ₃ . Further, since P ₂ O ₅ also has a problem of volatility and the like, the content of P ₂ O ₅ is 0.5% or less, preferably 0.1% or less.

The glass article may contain other components, for example, components derived from coloring agents and fining agents, as long as they do not affect the conditions of thermal processing and chemical strengthening. For example, when it is used as a cover glass having high transmittance, the content of TiO ₂ , SO ₃ , SnO, CeO ₂ , As ₂ O ₃ , and Sb ₂ O ₃ is 1% or less, preferably 0.5% or less. Further, the total content of these components is 1% or less, preferably 0.5% or less, more preferably 0.3% or less, further preferably 0.1% or less. Is preferred. However, it is preferable that As ₂ O ₃ and Sb ₂ O ₃ are not substantially contained because they have an adverse effect on the environment. It is preferable that the other components are not substantially contained.

Glass article _{further, ZrO 2, PbO, La 2} O 3, Y 2 O 3, MoO 3, WO 3, Nb 2 O 5, CoO, Cr 2 O 3 0.5%, respectively less, preferably 0. It may be contained in the range of 1% or less. The glass article may contain a noble metal element such as Au, Ag, Pt, Rh, and Os, and a halogen element such as Cl and F in a range of 0.5% or less for each element. However, it is preferable that the components listed from ZrO ₂ to Cr ₂ O ₃ , the noble metal element and the halogen element are not substantially contained. For example, ZrO ₂ causes corrosion of heat-resistant bricks in a melting kiln. The total content of the components TiO ₂ to F listed above is preferably 1% or less, more preferably 0.5% or less, and particularly preferably 0.1% or less.

[Characteristics of glass composition]
Hereinafter, preferable characteristics of the glass composition constituting the glass article will be described.

The glass composition whose composition has been described above has characteristics suitable for forming a three-dimensional shape by a mold pressing method performed at a relatively low temperature, specifically, a yield point, a glass transition point and a thermal expansion coefficient. obtain. These characteristics are as follows.

(The yield point At)
From the processing temperature condition of the mold pressing method, the upper limit of the yield point is 580 ° C., preferably 560 ° C. On the other hand, the lower limit of the yield point is 420 ° C, preferably 450 ° C, and more preferably 500 ° C.

(Glass transition temperature T _g )
From the mold release temperature condition of the mold pressing method, the upper limit of the glass transition temperature is 530 ° C., preferably 500 ° C. On the other hand, the lower limit of the glass transition temperature is 330 ° C, preferably 400 ° C, and more preferably 430 ° C.

(Coefficient of thermal expansion α)
In the mold pressing method, if the coefficient of thermal expansion of the glass composition is too large, it may be difficult to design a mold shape for obtaining a desired glass shape. Therefore, the thermal expansion coefficient α (unit: 10 ⁻⁷ / ° C.) is 80 to 120, preferably 80 to 100, as an average value from 50 ° C. to 350 ° C.

The glass composition preferably has a melting point, a working point, and a liquidus temperature suitable for producing a flat glass as a preform. There are various methods for producing flat glass, such as a float method and a down draw method, but the float method, which is a method for producing a large area flat glass with high productivity, is preferable.

When flat glass is obtained by the float method, it is desirable that the melting point T ₂ , working point T ₄ , and liquidus temperature _TL of the glass composition are as follows.

(Melting point T ₂ )
When the melting point is low, the amount of energy required to melt the glass raw material can be suppressed, and the glass raw material is more easily melted to promote defoaming and fining of the glass melt. The melting point is 1580 ° C or lower, preferably 1550 ° C or lower, and more preferably 1500 ° C or lower. The melting point T ₂ is the temperature at which the glass has a viscosity of 10 ² dPa · s, and may be displayed as T ₂ based on this viscosity. Also in the following, the numerical value indicated with T corresponds to the viscosity of the glass at that temperature.

(Working point T ₄ )
In the case of producing flat glass by the float method, the temperature of the molten glass is adjusted so that the viscosity η of the molten glass is about 10 ⁴ dPa · s when the molten glass is flowed into the float bath from the melting furnace. The lower the temperature (working point) at which the viscosity of the molten glass becomes 10 ⁴ dPa · s, the lower the working temperature is, for example, in order to thinly form the glass for a cover glass of a display, the working point is preferably 1300 ° C. or lower, Is 1200 ° C. or lower, and more preferably 1100 ° C. or lower. The lower limit of the working point is not particularly limited, but may be 800 ° C., for example.

(Liquid phase temperature (devitrification temperature) T _L )
When producing flat glass by the float method, it is necessary to avoid devitrification when the molten glass is formed into a flat shape. That is, it is preferable that the molten glass does not devitrify at the forming temperature (working point), in other words, the difference between the working point and the liquidus temperature is large. The difference between the working point and the liquidus temperature (T ₄ -T _L ) is preferably 10 ° C. or higher, preferably 50 ° C. or higher, more preferably 100 ° C. or higher.

[Method of manufacturing glass article]
(Formation of flat glass)
The glass article can be obtained by melting a glass raw material to form a flat glass plate, shaping the flat glass plate into a shape other than a flat plate by a mold pressing method, and further chemically strengthening the flat glass plate as necessary. The flat glass can be formed by a float method, a down draw method, or any other known method. As mentioned above, the float method is a preferred method for producing flat glass. Since the flat glass forming method including the float method is well known to those skilled in the art, the description thereof is omitted here.

(Mold press method)
In the mold pressing method, flat glass is press molded using a molding die. In this case, it is preferable to use an isothermal pressing method in which the forming die and the flat glass are heated to a predetermined temperature and pressed into a desired shape at that temperature (processing temperature). After press molding, the glass article is cooled to a predetermined temperature, the glass article is removed from the mold, and precision annealing is performed.

In the isothermal pressing method, the mold is heated to the temperature for processing flat glass, so it is required to have low strength at high temperatures and low reactivity with flat glass. Generally, a preform having a shape close to a desired product shape is relatively low by using a mold in which a surface of a cemented carbide is precisely processed and a release film such as a DLC (diamond-like carbon) film is coated on the surface. It is preferable to mold at the processing temperature. An example of the cemented carbide is tungsten carbide. If a mold made of cemented carbide is used, surface polishing after molding is unnecessary. On the other hand, when processing glass in a melt-softened state, a carbon-based material is used as a mold material because the processing temperature is high, but the surface processing accuracy is inferior to that of cemented carbide and deterioration of the release film. Due to the roughened surface, polishing tends to be required after pressing. Carbon-based materials have lower strength and poorer durability than cemented carbide.

In the case of producing a glass article having a three-dimensional shape by the mold pressing method using a flat glass as a preform, the mold and the flat glass are heated to a temperature exceeding the deformation point, while pressing the flat glass using the mold. It is preferable to hold for a predetermined time required for deformation (for example, 2 to 6 minutes, for example, 5 minutes), and then cool to a temperature around the glass transition point. When using a die in which a DLC film is coated on a cemented carbide, it is suitable to press at a processing temperature of 650 ° C. or lower, preferably 630 ° C. or lower in order to suppress wear of the DLC film. This condition is suitable for a method of forming a glass article in which the thickness t2 of the side plate portion 2 is substantially the same as the thickness t1 of the bottom plate portion 1 from a flat glass having a uniform thickness. On the other hand, particularly when the shape change due to thermal processing is large, if the processing temperature is too low, the viscosity η of the glass becomes large and the time required for deformation (holding time) becomes long. Therefore, an appropriate processing temperature is 550 ° C. or higher. The temperature is preferably 580 ° C or higher, more preferably 600 ° C or higher. When molding a glass article in which the thickness t2 of the side plate portion is larger than the thickness t1 of the bottom plate portion, it is preferable to set the processing temperature to, for example, 680 to 720 ° C, and further 700 to 715 ° C. In order to prevent the cooling time from becoming too long, the difference between the processing temperature and the mold release temperature is 150 ° C. or less, preferably 130 ° C. or less, more preferably 120 ° C. or less, further preferably 100 ° C. or less. ..

According to the mold press method, it is also possible to transfer the marks and the like to the surface of a glass article while molding it, by engraving marks or patterns on the part of the mold that contacts the flat glass.

(Chemical strengthening treatment)
Chemical strengthening is a technique of forming a compressive stress layer on the surface of a glass article by ion exchange in which the alkali metal ions contained on the surface of the glass article are replaced with monovalent alkali metal ions having a larger radius. Chemical strengthening is often carried out by replacing lithium ions (Li ⁺ ) with sodium ions (Na ⁺ ) or by replacing sodium ions with potassium ions (K ⁺ ).

The ion exchange can be performed by bringing the glass article into contact with a molten salt containing an alkali metal ion to be introduced on the surface of the glass article. The ion exchange may be carried out in two steps. For example, Na ⁺ introduced on the surface of the glass article by ion exchange with Li ⁺ may be further replaced by K ⁺ . Examples of the molten salt for ion exchange include potassium nitrate. A mixed molten salt of potassium nitrate and sodium nitrate is also a preferable molten salt.

The temperature of the molten salt brought into contact with the glass article is preferably 360 to 450 ° C. The contact time between the glass article and the molten salt is preferably 2 to 6 hours. The contact time is the time per ion exchange.

[Chemically strengthened glass articles]
In the glass article having the above-described glass composition, the glass composition before the ion exchange is maintained inside the surface except the surface affected by the ion exchange. A compressive stress layer is generated on the surface so as to include a portion affected by ion exchange. Therefore, in the chemically strengthened glass article, the glass composition before the chemical strengthening is maintained at least inside the compression stress layer. The entire glass article may have the composition described above.

The surface compressive stress C _S in the chemically strengthened glass article is 400 MPa or more, preferably 600 MPa or more, more preferably 800 MPa or more. The thickness DOC (Depth of Compression) of the compression stress layer is 60 μm or more, preferably 80 μm or more, more preferably 100 μm or more. DOC is the depth at which the stress inside the glass changes from compression to tension, that is, the depth at which the stress becomes 0 MPa. The ion exchange depth DOL (Depth of Layer) is preferably 5 to 12 μm. DOL is a depth at which birefringence can be confirmed, and can be measured using a glass surface stress meter (for example, FSM-6000 manufactured by Orihara Manufacturing Co., Ltd.).

Hereinafter, the present invention will be described in more detail with reference to Examples, but the following Examples are not intended to limit the present invention.

[Example 1]
(Production of glass)
A glass raw material batch was prepared by using ordinary glass raw materials such as silica sand, spodumene, alumina, lithium carbonate, sodium carbonate, potassium carbonate, dolomite, limestone, and iron oxide so that the glass composition shown in Example 1 of Table 2 was obtained. I prepared it. This batch was heated to 1550 ° C. with a platinum crucible and melted, and after holding for 4 hours as it was, molten glass was poured out onto an iron plate. The molten glass poured on the iron plate was solidified in 100 seconds, and immediately after solidification, it was placed in an electric furnace set at 600 ° C. After 30 minutes, the electric furnace was turned off, and the glass was obtained by allowing it to cool to room temperature and gradually cooling.

(Melting point T ₂ , working point T ₄ )
The high temperature viscosity of glass is measured using a platinum ball pull-up type automatic viscosity measuring device, and the melting point T ₂ is determined as the temperature at which the viscosity (η, unit is dPa · s) of the glass melt becomes 10 ² dPa · s. It was Similarly, the working point T ₄ was determined as the temperature at which the viscosity of the glass melt became 10 ⁴ dPa · s. The results are shown in Table 2.

(Liquid phase temperature _TL )
The obtained glass was crushed with an agate mortar, and the glass particles passed through a sieve having an opening of 2380 μm, and the glass particles retained on the 1000 μm sieve were sieved, and the glass particles were ultrasonically washed in ethanol and dried. The sample was used for liquidus temperature measurement. 25 g of this sample was weighed and transferred to a platinum boat having a width of 12 mm and a length of 200 mm, held in a temperature gradient furnace for 2 hours and taken out, and then the crystals (devitrification) formed in the glass were observed with an optical microscope. The maximum temperature at which crystals were observed was defined as the liquidus temperature (devitrification temperature) T _L. The results are shown in Table 2.

(Density ρ)
The obtained glass was cut into a size of 5 × 40 × 30 mm, each surface was mirror-polished to prepare a plate-like sample, and the density ρ of the glass was calculated from its weight. The results are shown in Table 2.

(Coefficient of thermal expansion α)
A cylindrical sample having a diameter of 5 mm and a length of 15 mm was prepared, and a glass transition temperature, a yield point and an average of 50 to 350 ° C. were measured by using a thermal expansion meter (thermomechanical analyzer TMA4110SA, manufactured by Bruker AXS KK). The linear expansion coefficient α was determined. The results are shown in Table 2.

(Softening point T _7.6 , sag point T ₁₀ , annealing point T ₁₃ , strain point T _14.5 and temperature-viscosity curve)
Using the obtained glass as a sample, a fiber elongation method (sample size: 10 mm diameter x 200 mm length round bar shape) or a beam bending method (sample size: 3 mm x 3 mm x) as disclosed in Non-Patent Document 4 is used. 55 mm square bar), softening point T _7.6 (η = 4.5 × 10 ⁷ dPa · s), sag point T ₁₀ (η = 10 ¹⁰ dPa · s), annealing point T ₁₃ (η = 10 ¹³ dPa · s) .S) and the strain point T _14.5 (η = 10 ^14.5 dPa · s) were measured. The results are shown in Table 5. FIG. 11 shows a melting point, a working point, and a temperature-viscosity curve prepared from these values using the Fruchar equation.

(Heat processing)
A glass plate having dimensions of 50 mm × 100 mm × 0.9 mm was prepared from the obtained glass, and both surfaces were mirror-polished to obtain a flat glass sample. The flat glass sample was heat-processed by the mold pressing method to obtain a glass sample having a three-dimensional shape similar to that shown in FIGS. A cemented metal mold having a DLC film coated thereon was used to form a dish-like shape having a depth of about 5 mm in which the side plate portion and the bottom plate portion had substantially the same thickness. Specifically, the mold and glass were heated with an infrared heater, the temperature was measured, the temperature was raised to the processing temperature (a predetermined temperature of 610 to 670 ° C.), and the pressure was maintained for 5 minutes. After that, it was cooled to a mold release temperature (500 ° C.), removed from the mold, annealed to 200 ° C. while being cooled, and left to stand at room temperature. Further, similarly to the above, the side plate portion was formed in a dish-like shape having a depth of about 5 mm, which was thicker than the bottom plate portion. The thickness of the bottom plate and the side plate of this sample were 0.6 mm and 1.3 mm, respectively. At this time, the sample was molded at a processing temperature of 710 ° C. and a holding time of 12 minutes. The average transmittance in the wavelength region of 400 to 1200 nm of the bottom plate portion of each of the obtained glass samples having a three-dimensional shape and the arithmetic average roughness Ra of the main surface corresponding to the bottom surface of the bottom plate portion were measured. The results are shown in Table 1. No decrease in transmittance due to devitrification was observed in the obtained glass sample having a three-dimensional shape. It was

Note that the average transmittance was determined by using a spectrophotometer (Hitachi U-4100 Spectrophotometer) and determining the average value of the transmittance measured every 5 nm in the wavelength range of 400 to 1200 nm. The arithmetic mean roughness Ra was measured twice using a stylus (Tencor Alpha-Step 500), with a needle diameter of 5 μm, a needle pressure of 10 mg, and a needle scanning speed of 50 μm / sec. Was determined by asking.

(Chemical strengthening treatment)
The glass sample having a three-dimensional shape was subjected to a two-step chemical strengthening treatment to obtain a chemically strengthened glass sample having a three-dimensional shape. The first chemical strengthening treatment was performed by using a mixed salt containing sodium nitrate (NaNO ₃ ) and potassium nitrate (KNO ₃ ) in a weight ratio of 6: 4, and immersing the sample in a molten salt bath kept at 420 ° C. for 5 hours. It was Subsequently, as the second chemical strengthening treatment, the sample was immersed in a potassium nitrate molten salt bath kept at 370 ° C. for 3 hours. The sample was taken out, cooled to room temperature, washed and dried.

(Stress distribution measurement)
In order to confirm the effect of chemical strengthening by thermal processing, the compressive stress distribution of the chemically strengthened sample obtained by thermal processing at 670 ° C was measured. Measurement of surface compressive stress C _S (unit: MPa) and compressive stress layer thickness DOC (unit: μm) using a stress distribution measuring device (FSM-6000 and SLP-1000 manufactured by Orihara Seisakusho) and measurement in the depth direction from the surface The compressive stress distribution was measured. CS was 980 MPa and DOC was 120 μm. The obtained stress distribution curve is shown in FIG. For comparison, the measurement results of a flat glass that has not been subjected to heat processing and chemically strengthened under the same conditions (Ref. Product) are also shown. It was observed that the curves overlap on the scale of FIG. A partially enlarged view is shown in FIG. It was observed that the difference was slight.

(Surface Na ion distribution)
The Na concentration distribution from the surface to the depth direction was evaluated using an X-ray microanalyzer equipped with a sputter etching function. The sample was used for stress distribution measurement. The results are shown in Fig. 14. It was confirmed that there was almost no difference in the concentration distribution of Na ions in the depth direction, just as there was almost no difference in the stress distribution in the depth direction (FIG. 12).

From the evaluation results of the compressive stress distribution and Na ion concentration distribution, it was confirmed that the effect of heat processing at 670 ° C on the chemical strengthening treatment was minor.

[Examples 2 to 23]
With respect to the glass compositions of Examples 2 to 23 in Tables 2 to 4, glass samples were prepared in the same manner as in Example 1, and the density ρ, the thermal expansion coefficient α, the yield point At, the glass transition point Tg, the melting point T ₂ , the working point were used. The results of measuring T ₄ and liquidus temperature TL are shown in Tables 2 to 4.

For Examples 2 and 3, the softening point T _{7.6 and the} like were also measured. The results are shown in Table 5. The temperature-viscosity curve is shown in FIG. In FIG. 11, reference numerals 11, 12, and 13 represent the measurement results of the glass compositions of Examples 1, 2, and 3, respectively. Curves 11 to 13 were temperature-viscosity curves suitable for application to the mold pressing method.

The table below shows the glass composition (mass% display) and various measurement results.

The glass article according to the present invention can be used for various purposes, for example, as a cover glass of a mobile terminal represented by a smartphone or a smart watch, a glass housing that houses the main body of the mobile terminal, and the like. The glass article according to the present invention can be used as, for example, a vehicle-mounted display device or a digital signage device. The glass article is not limited to being colorless and transparent, and may be colored by adding a coloring component especially when it is used as a glass housing.

Claims (12)

1. Has a shape other than a flat plate,
   Displayed in mass% based on oxide,
   SiO ₂ 60% or more, 70% or less,
   Al ₂ O ₃ 6% or more, 18% or less,
   Li ₂ O 2% or more, 8% or less,
   Na ₂ O 8% or more, 20% or less,
   K ₂ O 0% or more, 1% or less,
   MgO 0% or more, 3% or less,
   CaO 1% or more, 6% or less,
   A glass article having a glass composition containing 0.01% or more and 0.2% or less of Fe ₂ O ₃ .
2. A bottom plate portion, a side plate portion, and a bent portion,
   The glass article according to claim 1, having a shape in which the side plate portion is connected to the peripheral edge of the bottom plate portion via the bent portion.
3. The glass article according to claim 2, wherein the shape corresponds to at least one selected from a dish shape, a bat shape, and a box shape.
4. The glass article according to claim 2 or 3, wherein the side plate portion is thicker than the bottom plate portion.
5. The glass article according to any one of claims 2 to 4, wherein the bottom plate portion has a thickness of 0.3 mm or more and 2 mm or less.
6. The glass article according to any one of claims 1 to 5, wherein the content of Li ₂ O in the glass composition is 2% or more and 6.1% or less.
7. From the molten glass raw material, displayed by mass% of oxide standard,
   SiO ₂ 60% or more, 70% or less,
   Al ₂ O ₃ 6% or more, 18% or less,
   Li ₂ O 2% or more, 8% or less,
   Na ₂ O 8% or more, 20% or less,
   K ₂ O 0% or more, 1% or less,
   MgO 0% or more, 3% or less,
   CaO 1% or more, 6% or less,
   Forming a flat glass having a glass composition containing 0.01% or more and 0.2% or less of Fe ₂ O ₃ ;
   Molding the flat glass into a glass article having a shape other than a flat plate by a mold pressing method.
8. Has a shape other than a flat plate,
   Has a compressive stress layer on the surface,
   At least the portion other than the compressive stress layer is displayed by mass% based on oxide,
   SiO ₂ 60% or more, 70% or less,
   Al ₂ O ₃ 6% or more, 18% or less,
   Li ₂ O 2% or more, 8% or less,
   Na ₂ O 8% or more, 20% or less,
   K ₂ O 0% or more, 1% or less,
   MgO 0% or more, 3% or less,
   CaO 1% or more, 6% or less,
   A chemically strengthened glass article having a glass composition containing 0.01% or more and 0.2% or less of Fe ₂ O ₃ .
9. The chemically strengthened glass article according to claim 8, wherein the surface compressive stress is 400 MPa or more and the thickness of the compressive stress layer is 60 μm or more.
10. From the molten glass raw material, displayed by mass% of oxide standard,
    SiO ₂ 60% or more, 70% or less,
    Al ₂ O ₃ 6% or more, 18% or less,
    Li ₂ O 2% or more, 8% or less,
    Na ₂ O 8% or more, 20% or less,
    K ₂ O 0% or more, 1% or less,
    MgO 0% or more, 3% or less,
    CaO 1% or more, 6% or less,
    Forming a flat glass having a glass composition containing 0.01% or more and 0.2% or less of Fe ₂ O ₃ ;
    Forming the flat glass into a glass article having a shape other than a flat plate by a mold pressing method,
    A method for producing a chemically strengthened glass article, which comprises chemically strengthening the glass article.
11. A mobile terminal equipped with the glass article according to claims 1 to 6, 8 or 9.
12. A vehicle-mounted display device comprising the glass article according to any one of claims 1 to 6, 8 or 9.

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