WO2019017278A1 - Glass to be chemically strengthened and chemically strengthened glass - Google Patents

Abstract

The purpose of the present invention is to provide glass to be chemically strengthened which exhibits a thermal expansion coefficient and high-temperature viscosity which are of the same level as said coefficient and viscosity of conventional soda-lime glass, while making it possible to achieve high strength due to a chemical strengthening treatment. The present invention pertains to glass to be chemically strengthened which has a specific composition and exhibits an average linear thermal expansion coefficient of 75-95×10-7/K at 50-350°C.

Description

Chemical strengthening glass and chemically strengthened glass

The present invention relates to chemically strengthened glass.

Chemically strengthened glass is widely used as a cover glass or the like of an information device having a touch panel display. Chemically strengthened glass is formed by forming a compressive stress layer on the glass surface by ion exchange treatment. The properties of a chemically strengthened glass are usually expressed as surface compressive stress (CS) and depth of layer (DOL).

When the conventional soda lime glass is chemically strengthened, a chemically strengthened glass having a surface compressive stress CS of 400 to 600 MPa and a compressive stress depth DOL of about 6 to 10 μm can be obtained. However, such glasses have insufficient strength in some applications.

Therefore, in order to improve the strength of the chemically strengthened glass, an aluminosilicate glass which is susceptible to ion exchange has been developed. When the aluminosilicate glass is chemically strengthened, for example, a chemically strengthened glass having a CS of 700 to 850 MPa and a DOL of 20 to 100 μm can be obtained. However, aluminosilicate glass has poor productivity because of its high viscosity at high temperatures.

Therefore, conventionally soda lime glass Al ₂ O ₃ high content, soda lime glass having a high ion exchange performance, such as aluminosilicate glass has been proposed (see Patent Document 1).

International Publication No. 2014/122934

The glass described in Patent Document 1 has a high temperature viscosity equivalent to that of a conventional soda lime glass while containing more Al ₂ O ₃ than that of a conventional soda lime glass. This is considered to be due to the high content of the alkali metal oxide. Specifically, Na ₂ O is contained in an amount of 18 to 24% by mass, so that the thermal expansion coefficient is 95 × 10 ⁻⁷ / K or more. That is, the thermal expansion coefficient is larger than that of conventional soda lime glass. Therefore, there is a problem that dimensional change occurs due to temperature change when used in place of conventional soda lime glass.

An object of the present invention is to provide a glass for chemical strengthening, which has a thermal expansion coefficient similar to that of conventional soda lime glass and a high temperature viscosity similar to that of conventional soda lime glass, and high strength can be obtained by chemical strengthening treatment.

The present invention, in mass percentage based on oxides, SiO ₂ 62 ~ 68%, the _{Al 2 O 3 7 ~ 12%} , a Na ₂ O 15 ~ 18%, the _{K 2 O 0 ~ 2%,} MgO 7-12%, CaO 0-2%, ZrO ₂ 0.1-2%, the total amount of alkali metal oxides is 15-18%, and the total amount of alkaline earth oxides is 7-14%. A glass for chemical strengthening is provided, which has an average thermal expansion coefficient CTE of 75 to 95 × 10 ⁻⁷ / K at 50 ° C. to 350 ° C. The present invention also provides a chemically strengthened glass obtained from the above-mentioned glass for chemical strengthening.

According to the present invention, it is possible to obtain a glass for chemical strengthening which has a thermal expansion coefficient similar to that of conventional soda lime glass and a high temperature viscosity similar to that of conventional soda lime glass, and moreover high strength can be obtained by chemical strengthening treatment. In addition, a high-strength chemically strengthened glass having a thermal expansion coefficient similar to that of conventional soda lime glass and a similar high temperature viscosity can be obtained.

Hereinafter, the present invention will be described in detail, but the present invention is not limited to the following embodiments, and can be arbitrarily modified and implemented without departing from the scope of the present invention. In the present specification, when “%” is simply described, “mass%” is meant, and “...” means that the value is not less than the lower limit value and not more than the upper limit value.

The glass for chemical strengthening (untreated glass) of this embodiment is 62 to 68% of SiO ₂ , 7 to 12% of Al ₂ O ₃ , and 15 to 18% of Na ₂ O in terms of mass percentage on the basis of oxide. And 0 to 2% of K ₂ O, 7 to 12% of MgO, 0 to 2% of CaO, and 0.1 to 2% of ZrO ₂ . Here, the glass for chemical strengthening is an ion exchangeable glass and is a glass suitable for the chemical strengthening treatment.

The composition of this untreated glass will be described below.

SiO ₂ is a component constituting a glass network structure and is essential. In order to maintain the stability and weatherability of the glass, the content of SiO ₂ is 62% or more, preferably 63% or more, more preferably 63.5% or more. The content of SiO ₂ is 68% or less, preferably 67% or less, more preferably 66% or less, and still more preferably 65% or less, in order to lower the melting temperature of the glass to increase the productivity.

Al ₂ O ₃ is a component that improves ion exchange performance in chemical strengthening treatment, and is 7% or more, preferably 8% or more, more preferably 8 or more, in order to increase surface compressive stress CS after chemical strengthening. It is 5% or more, more preferably 9% or more. In the case of producing the present glass by the float method, the content of Al ₂ O ₃ is preferably 7% or more because tin can be prevented from entering the glass from the float bath during float molding.

In addition, the content of Al ₂ O ₃ is 12% or less, preferably 11% or less, more preferably 10% or less, and still more preferably 9% or less, in order to lower the devitrification temperature of the glass to facilitate forming. .

Na ₂ O is a component that forms a surface compressive stress layer by ion exchange in chemical strengthening treatment and is essential. The content of Na ₂ O is 15% or more, preferably 16% or more, more preferably 16.5%, in order to increase the surface compressive stress CS after chemical strengthening and to increase the compressive stress depth DOL. It is above. The content of Na ₂ O is at most 18%, preferably at most 17.5%, in order to maintain the weatherability of the glass.

Although not essential, K ₂ O can be contained up to 2% to increase the ion effect rate in the chemical strengthening treatment and to increase the compressive stress depth DOL after chemical strengthening. The content of K ₂ O is preferably 0.1% or more, more preferably 0.3% or more, in order to obtain the above-mentioned effects. When the content of K ₂ O is too large, it is difficult to increase the surface compressive stress CS after chemical strengthening. In addition, the thermal expansion coefficient may be increased. The content of K ₂ O is preferably 1.5% or less, more preferably 1% or less, and still more preferably 0.7% or less.

An alkali metal oxide selected from the group consisting of Li ₂ O, Na ₂ O and K ₂ O enhances the meltability of the glass while increasing the thermal expansion coefficient. Therefore, the total amount of these is 15 to 18%. In order to reduce the thermal expansion coefficient, it is preferably 17.5% or less.

The total amount of Na ₂ O and K ₂ O is preferably 15 to 18%, more preferably 17.5% or less.

In order to enhance the solubility while improving the chemical strengthening properties, it is preferable that the total content of Al ₂ O ₃ , ZrO ₂ and Na ₂ O be large: Al ₂ O ₃ + ZrO ₂ + Na ₂ O. Al ₂ O ₃ + ZrO ₂ + Na ₂ O is preferably 24.5% or more, more preferably 25% or more, still more preferably 25.5% or more, and particularly preferably 26% or more. On the other hand, when the content of Al ₂ O ₃ + ZrO ₂ + Na ₂ O is large, devitrification resistance and chemical durability deteriorate. In addition, the brittleness is deteriorated. Preferably it is 31% or less, more preferably 29% or less, still more preferably 28.5% or less, particularly preferably 28% or less.

Among the alkali metal oxides, Li ₂ O tends to reduce the surface compressive stress CS after chemical strengthening, so its content is preferably less than 1%, more preferably 0.1% or less, not contained Is preferred.

MgO is a component that enhances the stability of the glass, tends to improve the ion exchange performance for chemical strengthening, and contains 7% or more. The content of MgO is preferably 7.5% or more, more preferably 8% or more, in order to obtain a sufficient effect. If the content of MgO is too high, the glass is likely to be devitrified or the ion exchange rate in the chemical strengthening treatment is reduced. The content of MgO is 12% or less, preferably 11% or less, more preferably 10% or less, still more preferably 9% or less, in order to obtain the stability of the glass and the chemical strengthening treatment characteristics.

CaO is not essential but can be contained up to 2% to lower the high temperature viscosity of the glass. When the amount of CaO is too large, the glass tends to be devitrified and ion exchange is inhibited in the chemical strengthening treatment. The content of CaO is preferably 1% or less, more preferably 0.5% or less.

MgO, CaO, SrO and BaO are collectively referred to as alkaline earth oxides and are components that lower the high temperature viscosity of the glass to facilitate melting, and contain 7% or more in total. The total amount of the alkaline earth oxides is 14% or less, preferably 12% or less, more preferably 10% or less, and still more preferably 9% or less in order to suppress the devitrification and increase the ion exchange rate.

ZrO ₂ is contained in an amount of 0.1% or more, preferably 0.5% or more, more preferably 1% or more, in order to increase the surface compressive stress CS after chemical strengthening. If the ZrO ₂ content is too high, the liquidus temperature T _{L of the} glass may be too high. In order to maintain the stability of the glass, the ZrO ₂ content is 2% or less, preferably 1.5% or less, and more preferably 1% or less.

Untreated glass can contain other components as long as the object of the present invention is not impaired. The total content of the other components is preferably 4% or less, more preferably 1% or less, and still more preferably 0.5% or less. Below, the example of this other component is demonstrated.

For example, sulfates, chlorides, fluorides, etc. may be suitably contained as a fining agent at the time of glass melting.

It may also contain _Fe 2 _{O 3.} Since Fe ₂ O ₃ is abundantly present in nature, it is difficult to reduce the content to zero, and it is usually contained in an amount of 0.005% or more. Since Fe ₂ O ₃ produces blue or green coloration, 1% or less is preferable in order to suppress coloration, and 0.2% or less is more preferable.

It may contain TiO ₂ . Since TiO ₂ produces a yellow color, it is preferably 1% or less to inhibit coloration, more preferably 0.5% or less, and still more preferably 0.2% or less.

ZnO may be contained up to 2% to improve the meltability of the glass. However, when the glass is formed using the float method, it is preferable not to contain ZnO because ZnO is easily reduced in the float bath to cause defects in the product.

The average thermal expansion coefficient CTE at 50 ° C. to 350 ° C. of the untreated glass is 75 to 95 × 10 ⁻⁷ / K, as is the CTE of chemically strengthened glass. Since this CTE is comparable to conventional soda lime glass, when it is used by replacing it with conventional soda lime glass, dimensional deviation is not likely to occur even if the temperature changes, and it is easy to handle. The average thermal expansion coefficient CTE is preferably 94.5 × 10 ⁻⁷ / K or less. Further, it is preferably 80 × 10 ⁻⁷ / K or more, more preferably 85 × 10 ⁻⁷ / K or more.

The glass transition point Tg of the untreated glass is preferably 560 ° C. or more from the viewpoint of heat resistance. 570 ° C or more is more preferred at a point which is easy to obtain a desired shape, when curving and using untreated glass.

The temperature T _{2 at} which the viscosity of the glass is 10 ² dPa · s is preferably 1530 ° C. or less. Temperature T ₂ is an index of the production characteristics of the glass, which is a measure of the temperature required for dissolution of the glass material. The temperature T ₂ is more preferably 1525 ° C. or less. Also, typically, it is 1460 ° C. or higher.

The temperature T _{4 at} which the viscosity of the glass is 10 ⁴ dPa · s is preferably 1130 ° C. or less. Temperature T ₄ is an index of the production characteristics of the glass, which is a measure of the temperature for molding a glass. In order to increase the production efficiency of glass, the temperature T ₄ is more preferably 1120 ° C. or less, further preferably 1100 ° C. or less. Temperature T _4, it may become easily devitrified when molding the glass too low. To prevent devitrification upon molding, _{T 4} is preferably at least 1000 ° C., more preferably at least 1040 ° C., further preferably at least 1060 ° C..

Temperature T _4, the devitrification is likely to occur at too low a glass molded to the liquidus temperature T _L. Therefore, the difference T ₄ −T _L between the temperature T ₄ and the liquid phase temperature T _L is preferably −50 ° C. or more, more preferably −30 ° C. or more, and still more preferably −10 ° C. or more. When the float method is used for glass formation, T ₄ −T _L is preferably 0 ° C. or more, more preferably 10 ° C. or more, and still more preferably 20 ° C. or more.

The shape of the untreated glass is not particularly limited, but a plate-like shape is preferable in that the chemical strengthening treatment is easily performed. As a method for forming into a plate shape, known methods such as float method and fusion method can be applied. The float method is particularly preferable because high precision and large glass plates can be obtained efficiently. Although the plate thickness in the case of shape | molding in plate shape is not specifically limited, For example, they are 6 mm or less and 0.15 mm or more. For example, when the thickness is 1.3 mm or more, chemical strengthening can be performed after physical strengthening. 1.5 mm or more is preferable and, as for the plate thickness in that case, 1.8 mm or more is more preferable. Moreover, the plate thickness in the case of using for the laminated glass mentioned later is 1.1 mm or less, for example, 0.8 mm or less is preferable, and 0.5 mm or less is more preferable.

The present untreated glass may be used after being formed into a flat plate shape and then curved. In the case of bending, a flat plate-like glass is heated and bent using a mold or the like. It is also possible to make curved glass by laminating curved glass.

By chemically strengthening the above-mentioned untreated glass, chemically strengthened glass can be obtained.

The chemical strengthening treatment is a treatment for causing ion exchange between alkali metal ions in the glass and alkali metal ions in the molten salt by immersing the glass plate in the molten salt containing alkali metal ions having a large ion radius. Ion exchange occurs between alkali metal ions having a small ionic radius in the glass and alkali metal ions having a large ionic radius in the molten salt to form a compressive stress layer on the glass surface.

As a method of the chemical strengthening treatment, for example, the glass plate is immersed in a molten salt of potassium nitrate at 330 to 550 ° C. for 5 minutes to 20 hours. The processing conditions for the chemical strengthening are appropriately selected in consideration of the thermal characteristics of the glass, the application, the shape, and the like.

As a molten salt used for a chemical strengthening process, potassium nitrate, cesium nitrate, silver nitrate, potassium sulfate, potassium chloride, etc. are mentioned. These molten salts may be used alone, or a plurality of molten salts may be used in combination. Also, sodium salts may be added and used to adjust the chemical strengthening properties.

The chemically strengthened glass preferably contains, in the surface layer, at least one selected from the group consisting of potassium ions, cesium ions, rubidium ions and silver ions. The inclusion of these ions causes compressive stress on the surface. Moreover, when silver ion is contained, antimicrobial property is provided.

Chemically strengthened glass is provided with a compressive stress layer on its surface. The surface compressive stress CS is preferably 700 MPa or more. Chemically strengthened glass does not break even under strong tensile stress due to the large surface compressive stress.

The compressive stress depth DOL of the chemically strengthened glass is preferably 12 μm or more, more preferably 13 μm or more, still more preferably 15 μm or more, and particularly preferably 17 μm or more. Chemically tempered glass is likely to be broken when it is scratched at a depth exceeding DOL, so in order to prevent breakage, it is preferable that DOL be large. On the other hand, if the DOL is too large, cutting of the chemically strengthened glass becomes difficult. In order to be able to cut a chemically strengthened glass, the DOL is preferably 40 μm or less, more preferably 35 μm or less.

The surface compressive stress and the compressive stress depth can be measured by a surface stress meter.

The application of the chemically strengthened glass is not particularly limited. For example, it may be used for a cover glass of a portable display such as a mobile phone including a smartphone, a tablet type terminal, a cover glass of instruments, a cover glass of a cooking appliance, a lighting fixture, a showcase, and the like. In addition, it is suitable for double-layer glass for buildings and houses and for solar cell substrates.

The chemically strengthened glass of the present invention is also suitable as a laminated glass used in automobiles and the like. When using for laminated glass, it can also strengthen and bond after making an untreated glass curved. In addition, two chemically strengthened glass plates may be bonded, or a plate of the chemically strengthened glass may be bonded to another glass plate. A plate of this untreated glass may be attached.

In the following, Examples 1 to 19 are Examples, and Examples 20 to 24 are Comparative Examples. The glasses of Examples 1-17, 23 and 24 were made in the following manner. Examples 18 to 22 are calculation examples.

A common glass raw material is suitably selected so as to obtain the glass composition shown by mass percentage display in the SiO ₂ to ZrO ₂ columns of Tables 1 to 3, and a glass raw material prepared so as to obtain about 900 g of glass is platinum pot. The mixture was charged, melted for 4 hours in an electric furnace maintained at about 1600 ° C., and homogenized.

The obtained molten glass was poured into a mold and held at a temperature about 50 ° C. higher than the respective glass transition temperature Tg for 1 hour, and then cooled to about room temperature at a cooling rate of 1 K / min to obtain a glass block. The obtained glass block was cut, ground, and mirror-polished to obtain a 40 mm × 40 mm × 1 mmt glass plate (glass for chemical strengthening).

In addition, specific gravity, thermal expansion coefficient CTE, glass transition temperature Tg, temperatures T ₂ and T _4, and liquidus temperature T _L were measured by the method described later within the range that is possible using the remaining glass blocks. However, numerical values shown in parentheses are estimated values, and blanks indicate that they have not been evaluated. The results are shown in Tables 1 to 3.

The obtained glass plate was immersed in a molten salt at 425 ° C. consisting of 97.8% potassium nitrate and 2.2% sodium nitrate for 2.5 hours to obtain a chemically strengthened glass. The surface compressive stress CS and the compressive stress depth DOL were measured for the obtained chemically strengthened glass using a surface stress meter (FSM-6000) manufactured by Orihara MFG. However, the values shown in parentheses are estimated values. The results are shown in Tables 1 to 3.

The other evaluation methods are summarized below.

(Thermal expansion coefficient CTE and the glass transition point Tg)
The average thermal expansion coefficient at 50 ° C. to 350 ° C. was measured based on JIS R 1618 (2002) using a thermal expansion meter (TD5000 SA) manufactured by Bruker AXS, at a temperature rising rate of 5 K / min. Moreover, the glass transition point Tg was calculated | required from the obtained thermal expansion curve.

(specific gravity)
The specific gravity was measured by the Archimedes method.
(T ₂ and T ₄ )
T ₂ and _T 4 are based on ISO7884-2 (1987), was measured using a rotational viscometer.

(Liquid phase temperature T _L )
The glass was crushed using a mortar to obtain glass particles of 2 to 4 mm. The glass particles were placed on a platinum boat and held in a temperature ramp furnace for 24 hours. After cooling, the presence or absence of crystal precipitation was observed with a microscope. The maximum value of the temperature at which the glass particle in which the crystal was deposited was placed was taken as _TL .

As shown in Tables 1 to 3, Examples 1 to 19 which are Examples have thermal expansion coefficients and high temperature viscosity similar to those of conventional soda lime, and high strength was obtained by the chemical strengthening treatment.

On the other hand, in Comparative Examples 20 to 22, the content of the alkali metal oxide is large and the thermal expansion coefficient is large. Moreover, Example 23 which is a comparative example is an example of the aluminosilicate-based chemically strengthened glass, and since the content of Al ₂ O ₃ is large, T ₂ and T ₄ are high, and it can be seen that productivity is difficult. Although this glass provided high CS and very large DOL by chemical strengthening, it is difficult to cut after strengthening because DOL is too large.

Moreover, Example 24 which is a comparative example is an example of a conventional soda lime-based chemically strengthened glass, and since the content of Al ₂ O ₃ is small, the CS after strengthening is small, the DOL is also small, and the performance as a tempered glass is It is not enough.

Although the present invention has been described in detail with reference to particular embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present invention. The present application is based on the Japanese Patent Application (Japanese Patent Application No. 2017-139147) filed on July 18, 2017, which is incorporated by reference in its entirety. Also, all references cited herein are taken as a whole.

The chemically strengthened glass obtained from the glass for chemical strengthening of the present invention can be suitably used for a display device, particularly a cover glass of a touch panel display, and the like. In addition, it is suitable for double-layer glass for buildings and houses and for solar cell substrates.

Claims (9)

In mass percentage display of oxide standard,
62 to 68% of SiO ₂
7 to 12% of Al ₂ O ₃ ,
15 to 18% of Na ₂ O,
0 to 2% of K ₂ O,
7 to 12% of MgO,
0 to 2% of CaO,
Contains 0.1 to 2% of ZrO ₂ ,
The total amount of alkali metal oxides is 15 to 18%,
The total amount of alkaline earth oxides is 7 to 14%,
Chemical strengthening glass having an average linear thermal expansion coefficient of 75 to 95 × 10 ⁻⁷ / K at 50 ° C. to 350 ° C. Here, the alkali metal oxide is one or more selected from the group consisting of Li ₂ O, Na ₂ O and K ₂ O, and the alkali earth oxide is selected from the group consisting of MgO, CaO, SrO and BaO One or more selected. The glass for chemical strengthening according to claim 1, wherein the total content of Na ₂ O and K ₂ O is 15 to 18% in terms of mass percentage on an oxide basis. _Al 2 _O 3 in mass percentage based on oxides, the total content of ZrO ₂ and Na ₂ O is at least 25%, chemically strengthened glass according to claim 1 or 2. Temperature _{T 2} which the glass viscosity becomes ¹⁰ 2 dPa · s is 1530 ° C. or less, chemically strengthened glass according to any one of claims 1 to 3. Temperature _{T 4} which glass viscosity of ¹⁰ 4 dPa · s is 1130 ° C. or less, chemically strengthened glass according to any one of claims 1-4. The glass for chemical strengthening according to any one of claims 1 to 5, which is a float glass. A chemically strengthened glass obtained from the glass for chemical strengthening according to any one of claims 1 to 6. The chemically strengthened glass according to claim 7, having a surface compressive stress of 700 MPa or more. The chemically strengthened glass according to claim 7, wherein the compressive stress depth is 12 μm or more.