WO2015127583A1

WO2015127583A1 - Chemically toughened glass article with low coefficient of thermal expansion

Info

Publication number: WO2015127583A1
Application number: PCT/CN2014/072494
Authority: WO
Inventors: Huiyan Fan; Guangjun Zhang; Jose Zimmer; Chong Wang; Jochen Alkemper
Original assignee: Schott Ag; Schott Glass Technologies (Suzhou) Co., Ltd.
Priority date: 2014-02-25
Filing date: 2014-02-25
Publication date: 2015-09-03

Abstract

The invention provides a lithium-free boron alumino-silicate glass composition which is chemically toughened and a glass article manufactured thereof. The glass article has a CTE lower than 7.5 ppm/K^-1 at a temperature of 20 to 300°C, a Dol higher than 10 μm and a CS higher than 500 MPa. The glass article comprises a glass composition in accordance to the invention with the ratio R'O/R2O equal to or lower than 0.7 and wherein R' is at least one of Mg, Ca, Sr, Ba and wherein R is at least 10 one of Na and K. The non-bridge oxygen produced by alkali earth oxides can be controlled and the good chemical toughening properties (CS>500 MPa, Dol>10 μm) can be got. The glass has high thermal 15 shock resistance, high heat conductive coefficient and high surface tension. The chemical toughening low CTE glass article can be used as a cover for cellphones, smart phones, tablet PC, notebooks, PDA;20 or it can be used for flexible cover on folding screening display, OLED and the like.

Description

Chemically toughened glass article with

low coefficient of thermal expansion

Field of the invention

The invention relates to a lithium-free boron alumino-silicate glass composition for manufacturing a chemically toughened glass article, and to glass articles so manufactured. The glass composition is designed to meet the specific requirements arising form the intended use of the glass article, comprising the use of the glass article as a housing or to cover electronic devices or mobile electronic devices, such as televisions, personal data assistances, mobile or cellular telephones, watches, laptop computers and notebooks, digital cameras, PDAs and the like. Also such a glass article can be used as a touch-panel for such devices. The properties of the glass article comprising high thermal shock resistance, high heat conductivity and high surface tension are beneficial to reduce glass cracking risk during production and/or post treatment processes .

Background Chemically toughened glass is often used as a housing for electronic devices or mobile electronic devices, such as televisions, personal data assistances, mobile or cellular telephones, watches, laptop computers and notebooks, digital cameras, PDAs, displays and the like. Also such a glass article is often used for covering or to cover such electronic or mobile electronic devices or as a touch-panel for such electronic or mobile electronic devices. The special glass composition for such a glass article is to be selected according to the specific intended use. Important properties of such glass often comprise the depth of surface compressive layer (Dol) , surface compressive stress (CS) or the coefficient of thermal expansion (CTE) . The Dol and the CS are important properties in terms of the risk of cracks and the spreading of cracks, for example. In most cases, the cover glass must have high strength due to frequent contact. The touch sensitive glass of such devices is typically

chemically-strengthened.

Chemically strengthening of glass articles by ion exchange is well known in the art. The process involves exchange of alkali metal ions from within a surface layer on the glass article with different alkali metal ions from an external source. The typical practice is to operate at an elevated temperature that is below the glass strain point. In such a case, relatively large ions enter the glass and replace smaller ions in the glass by counter diffusion. This develops compressive stress in the ion-exchange surface layer on the article. In turns, the strength of the glass article is increased, and, consequently, so its resistance to fracture.

In detail, the chemical strengthening process requires immersion of glass substrate into a salt bath of a high temperature, and the process would require high thermal shock resistance of glass. Additionally, for many electronic or mobile electronic devices the glass article is becoming thinner and thinner with miniaturization is progressing. Such a cover glass is often referred to as a ultrathin glass. The chemical toughening of ultrathin glass creates additionally a high risk of warp of the glass substrate, i.e. the glass tends to warp or the glass bulgs during the manufacturing process. Warp arising during the toughening process of the thin glass can be reduced by designing a glass composition having an excellent heat conductivity as well as a low CTE . The thermal properties are of high importance when producing thin glass in order to reduce the temperature gradient between the tin surface and the air surface of the glass substrate during the forming process. In addition, the toughening process of the thin glass should be implemented on a low cost level, i.e. in a one step process ideally. Also, the new glass composition should be environmentally-friendly in terms of the mixture as well as the production process. A glass composition allowing to manufacture such a glass article is not known yet.

Regarding the usage of such a glass, a chemically toughened thin glass having a low CTE < 4ppm/K can be laminated with a TFT glass substrate directly. This method can reduce the thickness of electronic products and improve the output of brightness and fidelity on a LCD display.

US 4,554,259 A describes a kind of borosilicate glass with a CTE lower than 4.05 ppm/K at 20-200°C, densities less than 3.0 g/cm³ and can be produced by conventional continuous melting techniques. But the glass is alkali-free, and can't be chemically toughened and the strength is limited. This kind of glass is only used for photo-mask in semiconductor industry but can't be used as touch and cover glass due to the low strength.

EP 2 607 326 Al discloses an alkali-free glass, which is substantially free of alkali metal oxides, and has an average CTE of about 4-5.5 ppm/K at 30-380°C. The glass has properties sufficient for melting the glass at low costs. But the glass can't be chemically toughened to get high strength. So it only can be used as substrate plate of an OLED display but would not be a good choice for a display cover.

US 2013/0101853 Al discloses an alkaline earth

alumino-silicate glass with improved chemical and mechanical durability. The alkali oxide content is 5 mol % -12 mol % and a₂0/K₂0 may be included. K₂O may be present in an amount less than or equal to 0.5 mol %. The glass can be chemically toughened to improve the mechanical durability. But the content of alkaline earth being 8.0 mol % - 15 mol % is too high to get excellent chemical toughening properties. The chemical toughening process is not economical with temperature higher than 440 °C and toughening time longer than 8 hours.

Additionally, the content of B₂O₃ is less than 1 mol %, which is not beneficial to consume non-bridging oxygen in the glass structure .

Further, US 2012/0015197 Al discloses a boro-alumino-silicate glass which can be chemically toughened. The glass can be used for a protective glass material of high-grade electronic display products. But the CTE of the glass is high (>9.4ppm/K) and cracks maybe occur often during the annealing and the chemical toughening process. Additionally, the glass may be difficult to be formed to an ultra-thin glass due to the cracking caused by high CTE.

US 2010/0047521 Al describes a chemically toughened glass which can be used as a housing or to cover the components of a portable electronic device. The DoL is higher than 20ym and CS is higher than 400 MPa, but the CTE of the glass is higher than 7.5 ppm/K, which is not beneficial to the annealing and chemical toughening process. This glass is not free of AS₂O₃, which is not friendly to the environment. WO 2013/130665 A2 describes a low CTE, ion-exchangeable glass. The glass composition has a coefficient of thermal expansion which is less or equal to 5.5 ppm/K and is amenable to strengthening by ion-exchange. The glass composition is well suitable for use as the glass cladding layer of a laminated glass article. But the glass has a ratio of R'O/R^O, wherein R' is at least one of Mg, Ca, Sr, Ba; and wherein R is at least one of Li, Na, K, that is higher than 0.7, which results in high content of non-bridge oxygen and poor chemical toughening properties produced by high content of alkali earth oxides.

Finally, US 2011/0294649 Al discloses a glass composition having a low softening point and a high toughness. The glass has a low CTE and can be chemically toughened, but the glass is not totally lithium free. Because some of the glass containing lithium, two steps ion exchange process is necessary if high CS is obtained. The process of chemical toughening process is complicated and the time of chemical toughening is long, i.e. more than 10 hours.

Accordingly, one aspect of the invention is to provide a boron aluminosilicate glass having a relatively low CTE, being lower than 7.5 ppm/K at 20 - 300°C and that can be chemically toughened Therefore, the glass should have a Dol higher than 10 ym and a CS higher than 500 MPa .

Summary of the invention The present invention relates to a lithium free boron aluminosilicate glass article having a relatively low coefficient of thermal expansion. The glass article can be chemically toughened easily by ion exchange to increase the surface compression in the glass. The toughening can be performed under low temperature conditions and in a short time.

The glass composition is designed to meet the requirements for the manufacturability of a glass article consisting of such a glass composition. Also, the composition is designed to manufacture a glass article having specific properties that are advantageous for the special use intended. The special use intended comprises glass articles that can be used as a housing or cover for electronic devices, or mobile electronic devices, in particular for displays such as touch-panels. A glass article that is manufactured from a glass of such a glass composition in accordance to this invention may be formed to a sheet or 3D- or 2.5D-glass, respectively.

The task of the invention is solved by a boron aluminosilicate glass article for manufacturing a chemically toughened glass article, preferably a housing or cover of an electronic device or a mobile electronic device, wherein the glass composition of the glass article is substantially free of Lithium, and wherein the glass composition comprises:

Si0₂ from 40 mol % to 75 mol %;

A1₂0₃ from 8 mol % to 20 mol %;

Na₂0+K₂0 from 0.1 mol % to 20 mol %;

MgO+CaO+BaO+SrO from 0 mol % to 8 mol %;

Zr0₂ from 0 mol % to 5 mol %;

B₂0₃ from 1 mol % to 30 mol %;

Ce02 from 0 mol % to 1 mol %, wherein the ratio of R'O/R^O is equal or less than 0.7, preferably equal or less than 0.65 and more preferably equal or less than 0.6, R'O being the sum of MgO, CaO, SrO and BaO and R₂O being the sum of Na₂<3 and K₂O, and wherein R₂O > 0 and R'O >= 0.

The glass article is substantially free of Lithium, i.e. the amount of L1₂O is preferably equal or less than 1.0 mol ~6 , more preferably equal or less than 0.5 mol % and even more preferably equal or less than 0.1 mol %.

A glass having this glass composition is suitable for manufacturing a chemically toughened glass article being suitable as housing or cover for electronic devices or mobile electronic devices, in particular for displays, such as touch panels . The term substantially free", when used to describe the absence of a particular constituent in a glass composition, means that the constituent is present in the glass composition as a contaminant in a trace amount of less than 1 mol %, preferably less than 0.1 mol %.

The term CTE, as used within this document, refers to the coefficient of thermal expansion of the glass article averaged within a temperature range of between 20 and 300°C. The term CS, as used herein, refers to the surface compressive stress, i.e. the compressive stress is measured near the surface of the glass article. The CS is given in MPa, unless described otherwise. The term Dol, as used herein, refers to the depth of surface compressive layer, i.e. the area of layer, wherein alkali ions are exchanged. In the embodiments of the glass composition described herein, the concentration of specific components (e.g. S1O₂ and the like) is given in mol % (mole percent) on an oxide basis, unless described otherwise.

The balance of the constituents of the glass composition is of very high importance in order to manufacture a glass article with this composition having good properties for melting and chemical toughening on the one hand and also excellent properties in terms of a high thermal shock resistance, a high heat conductivity and a high surface tension. Accordingly, such a glass composition enables to manufacture a glass article having a high hardness and a high scratch-tolerance. Glass having a glass composition in accordance to the invention is characterized by favourable melting temperatures, i.e. it can be melted in standard glass tanks and formed by well-known processes such as a float-process. A glass article having the glass composition according to the invention has a glass transition temperature T_g of equal to or more than 550°C, preferably equal to or more than 570°C and more preferably equal to or more than 580°C. Such a relatively high glass transition temperature is advantageous for chemical toughening, as a thermal relaxation during the chemical toughening process is avoided.

The invention further comprises a method to manufacture a glass article of a glass comprising such a glass composition.

Within the glass composition, S1O₂ is the largest constituent of the glass composition and therefore, it is the largest primary constituent of the glass network. S1O₂ is important for the resistance of the glass on the one hand that can be increased with an increasing amount of Si0₂- A higher content of S1O₂ may increase the durability and mechanical strength of the glass, but it is also important to the melting capabilities on the other hand, wherein the formability may be diminished with higher concentrations of more than 75 mol %. Therefore, the content of S1O₂ is limited to 40 mol % and 75 mol %.

AI₂O₃ is also an important constituent for the glass composition since it may facilitate the ion exchange on the glass surface. A larger exchange depth of the ion exchange is favourable for the scratch-tolerance of the glass. In addition, it is an essential component for improving the chemical stability. Also, it may reduce the tendency for recystallization and may increase hardness of the glass. But, on the other hand, if the amount of AI₂O₃ is too high, the melting temperature may increase and the resistance to acids may decrease. AI₂O₃ may prevent non-bridging oxygen-functions (NBO) in the glass structure. Therefore, the content of AI₂O₃ is limited to 8 mol % and 20 mol %.

Zr0₂ may also improve the hardness of the glass. But, if the content is too high, the devitrification resistance of the glass deteriorates and the glass can easily form undissolved matter at the bottom of the glass tank. Therefore, the content of r0₂ is limited to 0 mol % and 5 mol %.

B₂O₃ is having a very positive influence on the

scratch-tolerance of the glass or glass article, respectively. Also, it is favourable to the melting properties of the glass. But, it may negatively influence the ion exchange. Therefore, the content of B₂O₃ is limited to 1 mol % and 30 mol %. When balanced out with other constituents, the content of B₂O₃ may exceed 2.5 mol %, preferably 3 mol % and even more preferably 3 mol %.

The glass composition also comprises alkali oxides R₂O, wherein R₂O is at least one of Na₂<3 and K₂O since the glass composition is substantially free of Li. The glass composition in accordance to the invention also comprises alkaline earth oxides R'O, wherein R'O is at least one of MgO, CaO, SrO, ZnO and BaO. R'O as well as R₂O are network transformers and therefore favourable to the melting properties of the glass.

The existence of Na-Ions and K-Ions is of high importance to the ion exchange; a glass without alkali oxides is not suitable for chemical toughening. K-Ions are advantageous for the exchange depth. Therefore, K₂O may be present to a specific amount within the glass composition. It has been found favourable to the properties of the glass article if the content of Na₂<3 is much higher than the content of K₂O, preferably higher by at least a factor 2 to increase the CS . It has been found that a higher content of Na₂<3 is also favourable for forming processes, in particular for floating or down-drawing. If the content of Na₂<3 and K₂O is too high, however, the glass viscosity may decrease. Therefore, the content of alkali oxides is carefully matched with the content of alkaline earth oxides.

The existence of alkaline earth oxides R'O may improve the melting behaviour by stabilizing the glass but increases the average CTE . MgO may not greatly affect the ion exchange by moderate use, wherein heavier constituents CaO, SrO or BaO as well as ZnO may influence the ion-exchange more, especially, if the content increases 2 mol %. The inventors have figured out that a glass composition is very well balanced if the ratio of R'O and R₂O is within a specific range. In detail, it is advantageous to the glass and the glass article, respectively, if the ratio of R'0/R₂0 of the glass composition is equal or less than 0.7, preferably equal or less than 0.65 and more preferably equal or less than 0.6, more preferably equal or less than 0.5, than more preferably equal or less than 0.4, than more preferably equal or less than 0.3, than more preferably equal or less than 0.2, than more preferably equal or less than 0.1.

A glass or a glass article manufactured of such a glass composition is characterized by properties that are excellent in terms of a high thermal shock resistance, a high heat conductive coefficient, a good glass melting quality, and a high surface tension. In addition, the addiction of the glass to warp during the manufacturing process can be reduced.

All these properties of the glass article are beneficial to reduce the risk of glass cracks during the production or manufacturing process and the post treatment processes, such as annealing, laser cutting or thermal cutting.

High thermal shock resistance is helpful to shorten the time of the annealing process during the manufacturing of the glass article and to shorten the time of the pre-heating or the post-annealing process during the chemical toughening process . The thermal shock resistance can be measured in accordance to the ISO 718.

High heat conductivity is suitable to reduce the temperature gradient between the tin-surface and the air-surface of the glass article during the manufacturing process in case of forming the glass by floating. Typically, a float glass can be formed in a float process with a tin bath. The tin-surface is the side of the glass that is in contact with the tin bath of the floating process, while the air-surface side of the glass is the opposite side of the tin-surface side.

High surface tension is beneficial to reduce bubbles and stripes in glass during clarification process. Summed up, the properties mentioned above are beneficial to reduce the risk of glass cracks during production processes and post treatment processes, such as annealing, laser cutting or thermal cutting process. For this reason, the productivity is high and the production yield of the glass article can be improved by the excellent thermal properties.

The glass article is characterized by a CTE at 20-300°C that is less than 7.5 ppm/K, preferably equal or less than 7.2 ppm/K, and more preferably equal or less than 7.0 ppm/K. Also, the glass article is characterized by a CTE at 20-300°C that is equal or more than 3.0 ppm/K, preferably equal or more than 3.5 ppm/K, and more preferably equal or more than 4.0 ppm/K.

In one embodiment, the glass composition of the glass article comprises B₂O₃ in a range of equal or more than 4 mol %, preferably equal or more than 4.4 mol % and more preferably equal or more than 5.0 mol %. In one additional embodiment, the glass composition of the glass article comprises B₂O₃ in a range of equal or more than 8 mol %. In this case, the balancing with the content of AI₂O₃ is of high importance.

An additional favourable condition for the glass composition has been found with respect to the contents of SiC>₂ and alkali oxides. The content of S1O₂ and the ratio to the content of alkali oxides is of importance when balancing the glass composition . It has been found favourable to the melting properties and the toughening properties of the glass if the ratio of

(Si0₂+B₂03+Al₂03) / ( a₂0+K₂0) of the glass composition is from 5 to 23, preferably from 6 tol7 and more preferably from 7 to 15, than more preferably from 8 to 14, than more preferably from 9 to 12.

One more condition refers to the ratio of alkali earth oxides R'O to alkali oxides R₂O. In a favourable embodiment, the ratio in glass composition is equal or less than 0.7, preferably equal or less than 0.65 and more preferably equal or less than 0.6. The R'O are negative to ion exchanging by producing non-bridge oxygen in glass structure. So the ratio should be controlled to be equal or lower than 0.7 to get excellent chemical toughening properties.

One more favourable additional condition belongs to the ratio of (Al₂0₃+CaO+MgO+SrO+BaO) to (B₂03+K₂0+ a₂0) of the glass composition (i.e. the ratio (Al₂0₃+CaO+MgO+SrO+BaO)

/ (B₂03+K₂0+ a₂0) ) . This value is advantageous if chosen to be from 0.1 to 1.8, preferably from 0.3 to 1.6 and more preferably from 0.4 to 1.5.

One further favourable condition relates to the ratio of ΣΟ/Σ (Si+Al+B) of the glass composition (i.e. the sum of the molar contents of oxygen divided by the sum of the molar contents of silicon, alumina) . This ratio is favourable from 1.0 to 2.5, preferably from 1.3 to 2.3 and more preferably from 1.5 to 2. This term describes the ratio between the total molar of oxygen and the molar content of (Si+AL+B) . This ratio influences the glass structure: if the value is becoming smaller, the glass structure becomes very loose and the glass has a higher CTE . When increasing the ratio too much, the glass structure is very compact, but the properties for chemical toughening become poor.

According to a further favourable embodiment, the contents of B₂0₃+MgO+CaO+SrO+BaO on the one hand and a₂0+K₂0+Al₂03 on the other hand are balanced. Specifically, it is advantageous if the ratio (B₂0₃+MgO+CaO+SrO+BaO) / ( a₂0+K₂0+Al₂0₃) is from 0 to 3.3, preferably from 0.1 to 3.1 and more preferably from 0.2 to 2.9.

One more condition refers to the content of alkali oxides R₂0. In a favourable embodiment, the content of R₂0 of the glass composition is equal or more than 4 mol %, preferably equal or more than 6 mol % and more preferably equal or more than 8 mol %, and wherein R₂0 is at least one of Na₂0 and K₂0. This increases the glass meltability.

A glass article manufactured by such a glass composition can be chemically toughened by an one stage ion exchange having a depth of layer (Dol) at 420°C for 6 hours that is equal or more than 8 ym, preferably equal or more than 10 ym and more preferably equal or more than 15 ym.

Such a glass article has a CS equal or more than 450 MPa, preferably equal or more than 500 MPa and more preferably equal or more than 550 MPa.

The strengthened glass article can be further processed by mechanical processing or etching or lithography or laser ablation or laser cutting or ion beam processing or printing to make detailed circuit according to the detailed application.

The glass article may have a heat conductivity λ equal or more than 0.9 W / (mK) , preferably equal or more than 1.01 / (mK) and more preferably equal or more than 1.1 W / (mK) .

The glass article may have a thermal shock resistance ΔΤ equal or more than 450 ^° C, preferably equal or more than 500 °C and more preferably equal or more than 640°C.

Further, the glass article may have a high surface tension o, which is defined as the molecule interaction on the surface of molten glass liquid, and wherein σ is equal or more than 200 * 10-3 N/m, preferably equal or more than 210 * 10-3 N/m and preferably equal or more than 220 * 10-3 N/m at melting temperature .

The chemical toughening of the glass can be performed easily by ion exchange. As used herein, the term "ion-exchange strengthened" means that a glass is strengthened by one or more ion-exchange processes. Such process might be known in the art of glass manufacturing. An ion-exchange process can include, but is not limited to, at least one surface of a glass article and at least one ion source. The glass articles are made using the one or more ion exchangeable colored glass compositions and/or one or more ion exchangeable, colorable glass compositions of this disclosure. The at least one ion source provides one or more ions having an ionic radius larger than the ionic radius of one or more ions present in at least one surface of the glass. In this manner, ions having smaller radii can replace or be exchanged with ions having larger radii in the at least one surface of the glass. Chemical toughening performance can be effected at a temperature within a range of temperatures at which ion inter-diffusion is sufficiently rapid within a reasonable time.

Also, typically such temperature is below the glass transition temperature (T_g) of the glass when it is desired that, as a result of such communication, a compressive stress (CS) . Such as lager ion radii K+ Rb+ or Cs+ replace smaller radii Na+ at temperatures between 430°C and 480°C for 1 to 10 hours and the depth of layer (Dol) are attained in the glass surface. Also, one or more colorants Au, Ag, Cu, Ni, Co, Fe, Mn, Cr, V, Ti, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu can be doped in molten KNO₃, RbNC>₃ or CSNO₃ in chemical toughening process. Different colors can be produced by the usage of different doped colorants. Additionally, antimicrobial properties can be got by Ag+, Zn2+, Cu+, Cu2+ ion exchanging on surface of the chemical toughening glass article.

The refractive index can be adjusted by ion exchange to match the lamination of sapphire. The refractive index n_d of sapphire is 1.76, which is much higher than the n_d of the glass article in accordance to this invention, that is from 1.50 to 1.51, so the lighting output is low caused by this mismatch. Ag can be diffused into glass surface to increase the refractive index n_d of the glass article. The refractive index can be increased to equal or more than 1.55, preferably equal or more than 1.6, and more preferably equal or more than 1.65. Similarly, one or more ions with high molecular refractive index such as Ba, Cs, Ba, Y, La, Bi, Pr, Te, Ge, Ti, Zr, Nb, Ta, W, Mn,Er, Yb, Lu can also increase the refractive index n_d by ion exchanging. On the other hand, surface crystallization can be formed by ion exchanging at high temperature of more than T_g. Such as the glass article is ion exchanging at a temperature of 700 to 900°C in molten mixture of L1₂SO₄ and K₂SO₄ for 3 hours, 1 hour, 30 minutes, 10 minutes or 5 minutes. Li+ and K+ diffuse into glass and β-spodumene can be formed on surface. The crystal size ranges from nanometer to micrometer-size and transparent, translucent or opaque glass ceramic can be formed under different heat treatment. Hardness, strength and scratch resistance can be improved by crystallization.

For using a glass of such composition as a housing for or to cover electronic or mobile electronic devices, the glass article can be formed to a sheet glass as well as a thin or ultrathin glass having a thickness of about equal or less than 1.0 mm, equal or less than 0.5 mm, equal or less than 0.3 mm, equal or less than 0.1 mm, equal or less than 0.05 mm, equal or less than 0.03 mm.

A glass in accordance to the invention can be formed by float, micro-float, down-draw slot-draw, or fusion-draw. The glass can be cut by laser, by blade, by multiple wire, by water before or after the chemical toughening process. The glass can be formed to 3D- or to 2.5D- shapes by precision molding methods.

In one preferred embodiment, a glass article in accordance to the inventions comprises the following glass composition and conditions :

The invention further relates to a method for manufacturing a boron aluminosilicate glass article from a glass comprising a glass composition in accordance to the invention. The glass article can be formed to a glass by float, micro-float, down-draw slot-draw, or fusion-draw.

The glass article may have a thickness of about equal or less than 1.0 mm, equal or less than 0.5 mm, equal or less than 0.3 mm, equal or less than 0.1 mm, equal or less than 0.05 mm, equal or less than 0.03 mm.

The glass article may be pre-heated at a temperature of 300 to 400°C, wherein the time of pre-heating can be limited to 30 minutes, 20 minutes, 10 minutes or even 5 minutes only. Then the glass article can be chemically toughened in molten salt, wherein the chemical toughening temperature is from 350°C to 490°C and the time for chemical toughening is in a range of about

1 and 16 hours.

The chemical toughening temperature may also be from from 400 to 480 °C with a chemical toughening time in a range of about

2 and 8 hours .

Finally, a post-annealing may take place at a temperature from 300 to 400°C and the time of post-annealing can be limited to 30 minutes, 20 minutes, 10 minutes or even 5 minutes.

The glass can be screen-printed in order to get a specific design . A glass article manufactured in such a process may be characterized by the following properties : a high thermal shock resistance, a high heat conductive coefficient and a high surface tension. All of these properties are beneficial to reduce glass cracking probabilities during production process and post treatment, such as annealing, laser cutting or thermal cutting process.

The properties of the glass article are determined by the glass composition and structure; i.e. the proper glass network structure is benefit to the ion exchange during chemical toughening .

Having such properties, a glass article manufactured by a glass of a glass composition in accordance to this invention is suitable for use as a housing for electronic devices or mobile electronic devices, such as televisions, personal data assistances, mobile or cellular telephones, watches, laptop computers and notebooks, digital cameras, PDAs, displays and the like. Also such a glass article can be used ideally for covering or to cover such electronic or mobile electronic devices, e.g. for a touch-panel. The CTE of a chemical toughening glass article in accordance with this invention can be matched with sapphire (5 to 6.7 ppm/K) . The chemical toughening glass article can be laminated with sapphire directly or indirectly. In one preferred embodiment, lapping and polishing of both sides of the glass article can be performed wherein the CTE is in a range of 3 to 7.5 ppm/K, preferably in a range of 5 to 6.7 ppm/K and more preferably in a range of 5.5 to 6.5 ppm/K. Then the glass article can be put on a sapphire. This two layer lamination can be heated in a muffle furnace at a temperature of 850°C to 950°C and the glass article can be fused to sapphire sheet. Then, this lamination assembly can be chemically toughened in molten pure KNO3 at a temperature of 390 to 450°C, the chemical toughening time could be from 1 to 10 hours, preferably from 400 to 430°C for 5 to 8 hours, and more preferably at 420°C for 6 hours, so that the top side of the glass article is toughened. A high CS and Dol can be achieved with a CS of more than 500 MPa and a Dol of more than 10 ym. Such as glass may have the following composition:

Si0₂ 62.9 mol %,

AI₂O₃ 14.18 mol %,

Na₂0 8.02 mol %,

K₂0 3.11 mol %,

MgO 6.23 mol %,

B₂0₃ 5.4 mol %, wherein the CTE is 6.34 ppm/K. This glass can be laminated with sapphire at a temperature of 730 to 750°C for 30 minutes. Then this glass can chemically toughened at 420°C for 6 hours to get a high CS of 673 MPa and a Dol of 27 ym on the top side of the glass.

In one more preferred embodiment, lapping and polishing of both sides of the glass article can be performed wherein the CTE is in range of 3 to 7.5 ppm/K, preferably in a range of 5 to 6.7 ppm/K and more preferably in a range of 5.5 to 6.5 ppm/K. Then this glass article can chemically be toughened in molten pure at a temperature of 390 to 450°C, chemical toughening time is from 1 to 10 hours, preferably at a temperature of 400 to 430°C for 5 to 8 hours, more preferably at a temperature of 420°C for 6 hours in molten KNO3 to get a CS of more than 500 MPa and a Dol of more than 10 ym.

The glass article can be adhered to sapphire by glass powder. This three layer lamination assembly can be heated and sealed at a temperature below 400°C, more preferably below 380°C, than more preferably below 370°C, than more preferably below 350°C, than more preferably below 300 °C. This chemical toughening glass article can be adhered to a sapphire sheet by the fused glass powder. In one additional preferred embodiment, lapping and polishing of both sides of the glass article can be performed wherein the CTE is in range of 3 to 7.5 ppm/K, preferably in a range of 5 to 6.7 ppm/K and more preferably in a range of 5.5 to 6.5 ppm/K. Then the glass article can be chemically toughened in molten pure KNO3 at a temperature of 390 to 450°C, the chemical toughening time is from 1 to 10 hours, preferably at a temperature of 400 to 430°C for 5 to 8 hours, and more preferably at a temperature of 420°C for 6 hours in molten KNO3 to get a CS of more than 500 MPa and a Dol of more than lOym. The glass article can be adhered to sapphire by optical clear adhere (OCA) , then the lamination can be sealed by UV irradiation for 30 minutes. The chemical toughening glass article can be adhered to sapphire sheet by the optical clear adhere (OCA) .

Additionally, a thin or ultra-thin glass article can be made, that can be used on the thinner non-air gap electronic equipment. Designing the glass composition of the glass article in advance for the special use intended, a glass according to the invention helps to receive a cover glass that matches the requirements given by the application, i.e. the display which should be covered, for example. Finally, a glass article can be processed easily by laser cutting. Also, in order to produce a sense touch with electrodes, an Indium-Tin-oxide-layer (ITO-layer) can be deposited on the back of the glass article. It can be patterned to create the electrodes .

The glass article can be used on one glass solution (OGS) with better edge quality. Such a glass with a low CTE further may help to reduce pre-heating and post-annealing times in order to increase production efficiency of the chemical toughening process . This is important especially when producing thin glass or ultra thin glass.

The following tables specify in total 47 examples of glass compositions, conditions and properties relating to a boron aluminosilicate glass in accordance to this invention. Constituent Example 1 Example 2 Example 3 mol% mol% mol%

Si0₂ 67.33 65.33 67.86

Al₂0₃ 17.20 17.20 14.97

Na₂0 7.15 7.15 7.99

K₂0 0.25 0.25 0.20

MgO 0.00 0.00 0.00

Zr0₂ 0.39 0.39 0.00

Ce0₂ 0.04 0.04 0.00

Sn0₂ 0.14 0.14 0.00

B₂0₃ 7.50 9.50 8.98

CaO 0.00 0.00 0.00

BaO 0.00 0.00 0.00

Na₂0+K₂0 7.40 7.40 8.19

(MgO+CaO+SrO+BaO)/(Na20+K20) 0.00 0.00 0.00

(Si0₂+B₂0₃+AI₂0₃)/(Na₂0+K₂0) 12.44 12.44 11.21

(AI₂0₃+CaO+MgO+SrO+BaO)/(B₂0₃+K₂0+Na₂0) 1.15 1.02 0.87

∑0/∑(Si+AI+B) 1.86 1.84 1.86

(B₂0₃+MgO+CaO+SrO+BaO)/(Na₂0+K₂0+AI₂0₃) 0.30 0.39 0.39

Surface Tension(10^"3 N/m) 300 253 282

Heat Conductivity W/(mK) 1.15 1.10 1.13

Tg (°C) 685 662 639

CTE(ppm/K) 4.18 4.36 4.79

AT(°C) 790 758 745

CS( MPa ) 650

ϋοΙ(μΓπ ) 24

Constituent Example Example Example Exami

4 5 6 7 mol% mol% mol% mol%

Si0₂ 66.70 65.96 66.27 66.18

Al₂0₃ 16.91 16.74 16.66 16.29

Na₂0 8.09 8.15 8.83 9.07

K₂0 0.30 0.29 0.21 0.22

MgO 0.00 0.00 0.00 0.00

Zr0₂ 0.00 0.00 0.00 0.00

Ce0₂ 0.00 0.00 0.00 0.04

Sn0₂ 0.00 0.00 0.00 0.17

B₂0₃ 8.00 8.86 8.03 8.03

CaO 0.00 0.00 0.00 0.00

BaO 0.00 0.00 0.00 0.00

Na₂0+K₂0 8.39 8.44 9.04 9.29

(MgO+CaO+SrO+BaO)/(Na₂0+K₂0) 0.00 0.00 0.00 0.00

(Si0₂+B₂0₃+AI₂0₃)/(Na₂0+K₂0) 10.92 10.85 10.06 9.74

(AI₂0₃+CaO+MgO+SrO+BaO)/(B₂0₃+K₂0+Na₂0) 1.03 0.97 0.98 0.94

∑0/∑(Si+AI+B) 1.86 1.85 1.86 1.87

(B₂0₃+MgO+CaO+SrO+BaO)/(Na₂0+K₂0+AI₂0₃) 0.32 0.35 0.31 0.31

Surface Tension(10^"3 N/m) 293 290 318 289

Heat Conductivity W/(mK) 1.13 1.12 1.12 1.12

Tg (°C) 651 649 655 648

CTE (ppm/K) 5.20 4.86 4.96 5.12

A (°C) 758 753 761 758

CS ( MPa ) 680

Dol (ym) 28

Example Example Example Example

8 9 10 11 mol% mol% mol% mol%

Constituent

Si0₂ 68.61 71.11 66.92 63.25

Al₂0₃ 15.74 14.52 17.15 13.00

Na₂0 8.97 9.52 9.77 9.00

K₂0 0.50 0.25 0.60 1.50

MgO 0.00 0.00 0.00 0.00

Zr0₂ 0.00 0.39 0.00 0.00

Ce0₂ 0.04 0.04 0.04 0.05

Sn0₂ 0.17 0.17 0.17 0.10

B₂0₃ 5.97 4.00 5.36 13.10

CaO 0.00 0.00 0.00 0.00

BaO 0.00 0.00 0.00 0.00

Na₂0+K₂0 9.47 9.77 10.36 10.50

(MgO+CaO+SrO+BaO)/(Na₂0+K₂0) 0.00 0.00 0.00 0.00

(Si0₂+B₂0₃+AI₂0₃)/(Na₂0+K₂0) 9.54 9.17 8.63 8.51

(AI₂0₃+CaO+MgO+SrO+BaO)/(B₂0₃+K₂0+Na₂0) 1.02 1.05 1.09 0.55

∑0/∑(Si+AI+B) 1.89 1.93 1.89 1.86

(B₂0₃+MgO+CaO+SrO+BaO)/(Na₂0+K₂0+AI₂0₃) 0.24 0.16 0.19 0.56

Surface Tension(10^"3 N/m) 274 317

Heat Conductivity W/(mK) 1.11 1.11

Tg (°C) 675 701 569

CTE (ppm/K) 5.37 5.30 5.12 6.27

A (°C) 783 827 683

CS ( MPa ) 700 560

Dol (ym) 25 22

Constituent Example Example Example Exampl

12 13 14 e 15 mol% mol% mol% mol%

Si0₂ 68.00 67.86 67.32 65.94

Al₂0₃ 17.53 15.47 17.19 12.82

Na₂0 10.00 9.98 10.14 10.54

K₂0 0.53 0.80 1.25 1.50

MgO 0.00 0.00 0.00 0.00

Zr0₂ 0.00 0.00 0.39 0.00

Ce0₂ 0.00 0.04 0.04 0.04

Sn0₂ 0.00 0.17 0.17 0.17

B₂0₃ 3.94 5.69 3.50 8.99

CaO 0.00 0.00 0.00 0.00

BaO 0.00 0.00 0.00 0.00

Na₂0+K₂0 10.53 10.78 11.39 12.04

(MgO+CaO+SrO+BaO)/(Na₂0+K₂0) 0.00 0.00 0.00 0.00

(Si0₂+B₂0₃+AI₂0₃)/(Na₂0+K₂0) 8.50 8.26 7.73 7.29

(AI₂0₃+CaO+MgO+SrO+BaO)/(B₂0₃+K₂0+Na₂0) 1.21 0.94 1.15 0.61

∑0/∑(Si+AI+B) 1.90 1.91 1.92 1.91

(B₂0₃+MgO+CaO+SrO+BaO)/(Na₂0+K₂0+AI₂0₃) 0.14 0.22 0.12 0.36

Surface Tension(10^"3 N/m)

Heat Conductivity W/(mK)

Tg (°C) 706 604

CTE (ppm/K) 5.11 5.26 6.04 7.24

A (°C) 821 724

CS ( MPa )

Dol (ym)

Example Example Example Example

16 17 18 19 mol% mol% mol% mol%

Constituent

Si0₂ 66.86 65.86 71.19 68.00

Al₂0₃ 17.96 16.96 4.64 12.00

Na₂0 11.97 12.97 7.14 9.00

K₂0 0.50 0.80 7.65 0.80

MgO 0.00 0.00 0.00 0.11

Zr0₂ 0.00 0.00 0.00 0.00

Ce0₂ 0.04 0.04 0.00 0.00

Sn0₂ 0.17 0.17 0.00 0.09

B₂0₃ 2.49 3.19 9.38 10.00

CaO 0.00 0.00 0.00 0.00

BaO 0.00 0.00 0.00 0.00

Na₂0+K₂0 12.47 13.77 14.79 9.80

(MgO+CaO+SrO+BaO)/(Na₂0+K₂0) 0.00 0.00 0.00 0.01 (Si0₂+B₂0₃+AI₂0₃)/(Na₂0+K₂0) 7.00 6.25 5.76 9.18 (AI₂0₃+CaO+MgO+SrO+BaO)/(B₂0₃+K₂0+Na₂0) 1.20 1.00 0.19 0.61 ∑0/∑(Si+AI+B) 1.93 1.94 2.01 1.89

(B₂0₃+MgO+CaO+SrO+BaO)/(Na₂0+K₂0+AI₂0₃) 0.08 0.10 0.48 0.46 Surface Tension(10^"3 N/m) 328 Heat Conductivity W/(mK) 1.15

Tg (°C) 608 CTE (ppm/K) 5.71 6.18 7.20 5.78 A (°C) 723 CS ( MPa ) 685 Dol (ym) 21

Example Example Example Exa

Constituent 20 21 22 23 mol% mol% mol% mol%

Si0₂ 69.92 68.00 66.86 64.53

Al₂0₃ 12.99 12.00 14.97 17.80

Na₂0 8.99 8.00 10.98 7.22

K₂0 0.80 0.80 0.60 0.25

MgO 0.50 0.51 1.40 1.13

Zr0₂ 0.60 0.60 0.00 0.39

Ce0₂ 0.04 0.00 0.04 0.04

Sn0₂ 0.17 0.09 0.17 0.14

B₂0₃ 5.99 10.00 4.99 8.50

CaO 0.00 0.00 0.00 0.00

BaO 0.00 0.00 0.00 0.00

Na₂0+K₂0 9.79 8.80 11.58 7.47

(MgO+CaO+SrO+BaO)/(Na₂0+K₂0) 0.05 0.06 0.12 0.15 (Si0₂+B₂0₃+AI₂0₃)/(Na₂0+K₂0) 9.08 10.23 7.50 12.16 (AI₂0₃+CaO+MgO+SrO+BaO)/(B₂0₃+K₂0+Na₂0) 0.85 0.67 0.99 1.19 ∑0/∑(Si+AI+B) 1.93 1.90 1.93 1.86

(B₂0₃+MgO+CaO+SrO+BaO)/(Na₂0+K₂0+AI₂0₃) 0.29 0.51 0.24 0.38 Surface Tension(10^"3 N/m) 312 260 305 Heat Conductivity W/(mK) 1.10 1.14 1.15

Tg (°C) 674 616 692 CTE (ppm/K) 5.75 5.51 5.54 4.26 A (°C) 797 733 784 CS ( MPa ) 630

Dol (ym) 29

Example Example Example Example

Constituent 24 25 26 27 mol% mol% mol% mol%

Si0₂ 68.69 65.84 64.25 63.37

Al₂0₃ 11.16 12.25 14.00 12.67

Na₂0 7.89 10.02 7.00 8.67

K₂0 0.00 0.81 1.50 2.99

MgO 0.41 2.37 2.10 3.11

Zr0₂ 0.60 0.00 0.00 0.00

Ce0₂ 0.00 0.04 0.05 0.04

Sn0₂ 0.09 0.17 0.10 0.12

B₂0₃ 10.35 8.50 11.00 9.04

CaO 0.40 0.00 0.00 0.00

BaO 0.40 0.00 0.00 0.00

Na₂0+K₂0 7.89 10.83 8.50 11.66

(MgO+CaO+SrO+BaO)/(Na₂0+K₂0) 0.15 0.22 0.25 0.27 (Si0₂+B₂0₃+AI₂0₃)/(Na₂0+K₂0) 11.43 7.99 10.50 7.29 (AI₂0₃+CaO+MgO+SrO+BaO)/(B₂0₃+K₂0+Na₂0) 0.68 0.76 0.83 0.76 ∑0/∑(Si+AI+B) 1.90 1.93 1.87 1.93

(B₂0₃+MgO+CaO+SrO+BaO)/(Na₂0+K₂0+AI₂0₃) 0.61 0.47 0.58 0.50 Surface Tension(10^"3 N/m) 317 280

Heat Conductivity W/(mK) 1.15 1.13

Tg (°C) 605 614 593 CTE (ppm/K) 4.36 6.46 5.38 7.11 A (°C) 718 718 688 CS ( MPa ) 735 533 712 Dol (ym) 25 17 30

Example Example Example Exarnpl

Constituent 28 19 30 31 mol% mol% mol% mol%

Si0₂ 63.06 65.94 65.00 66.33

Al₂0₃ 12.61 14.97 12.81 14.25

Na₂0 8.63 7.98 9.53 9.22

K₂0 2.98 0.50 0.50 0.25

MgO 3.09 2.41 3.00 2.88

Zr0₂ 0.48 0.00 0.00 0.39

Ce0₂ 0.04 0.04 0.04 0.04

Sn0₂ 0.12 0.17 0.12 0.14

B₂0₃ 9.00 7.98 9.00 6.50

CaO 0.00 0.00 0.00 0.00

BaO 0.00 0.00 0.00 0.00

Na₂0+K₂0 11.61 8.48 10.03 9.48

(MgO+CaO+SrO+BaO)/(Na₂0+K₂0) 0.27 0.28 0.30 0.30

(Si0₂+B₂0₃+AI₂0₃)/(Na₂0+K₂0) 7.29 10.48 8.66 9.19

(AI₂0₃+CaO+MgO+SrO+BaO)/(B₂0₃+K₂0+Na₂0) 0.76 1.06 0.83 1.07

∑0/∑(Si+AI+B) 1.94 1.89 1.92 1.93

(B₂0₃+MgO+CaO+SrO+BaO)/(Na₂0+K₂0+AI₂0₃) 0.50 0.44 0.53 0.40

Surface Tension(10^"3 N/m) 278 287 273

Heat Conductivity W/(mK) 1.13 1.13 1.12

Tg (°C) 587 618 657

CTE (ppm/K) 7.33 4.61 6.15 5.78

A (°C) 676 730 767

CS ( MPa ) 645

Dol (ym) 28

Example Example Example Exarnpl

Constituent 32 33 34 35 mol% mol% mol% mol%

Si0₂ 69.00 64.90 64.90 80.67

Al₂0₃ 14.00 12.18 12.18 2.69

Na₂0 6.00 9.02 9.02 4.62

K₂0 0.50 1.11 1.11 0.60

MgO 2.00 3.23 3.23 0.00

Zr0₂ 0.00 0.00 0.00 0.00

Ce0₂ 0.00 0.04 0.04 0.00

Sn0₂ 0.09 0.12 0.12 0.00

B₂0₃ 8.41 9.40 9.40 9.75

CaO 0.00 0.00 0.00 1.67

BaO 0.00 0.00 0.00 0.00

Na₂0+K₂0 6.50 10.13 10.13 5.22

(MgO+CaO+SrO+BaO)/(Na₂0+K₂0) 0.31 0.32 0.32 0.32

(Si0₂+B₂0₃+AI₂0₃)/(Na₂0+K₂0) 14.06 8.54 8.54 17.84

(AI₂0₃+CaO+MgO+SrO+BaO)/(B₂0₃+K₂0+Na₂0) 1.07 0.79 0.79 0.29

∑0/∑(Si+AI+B) 1.88 1.92 1.92 1.95

(B₂0₃+MgO+CaO+SrO+BaO)/(Na₂0+K₂0+AI₂0₃) 0.51 0.57 0.57 1.44

Surface Tension(10^"3 N/m) 331 310 292 297

Heat Conductivity W/(mK) 1.15 1.14 1.17 1.14

Tg (°C) 666 598 604 588

CTE (ppm/K) 4.17 6.20 6.55 4.41

A (°C) 776 701 690 684

CS ( MPa ) 676 668

Dol (ym) 20 22

Example Example Example Exarnpl

Constituent 36 37 38 39 mol% mol% mol% mol%

Si0₂ 63.31 61.25 62.90 60.30

Al₂0₃ 12.74 12.00 13.18 15.00

Na₂0 9.63 10.00 9.02 11.40

K₂0 2.03 1.50 2.11 1.60

MgO 3.92 4.10 4.23 5.00

Zr0₂ 0.00 0.00 0.00 0.49

Ce0₂ 0.04 0.05 0.04 0.04

Sn0₂ 0.17 0.10 0.12 0.17

B₂0₃ 8.17 11.00 8.40 6.00

CaO 0.00 0.00 0.00 0.00

BaO 0.00 0.00 0.00 0.00

Na₂0+K₂0 11.67 11.50 11.13 13.00

(MgO+CaO+SrO+BaO)/(Na₂0+K₂0) 0.34 0.36 0.38 0.38

(Si0₂+B₂0₃+AI₂0₃)/(Na₂0+K₂0) 7.22 7.33 7.59 6.25

(AI₂0₃+CaO+MgO+SrO+BaO)/(B₂0₃+K₂0+Na₂0) 0.84 0.72 0.89 1.05

∑0/∑(Si+AI+B) 1.95 1.93 1.94 1.98

(B₂0₃+MgO+CaO+SrO+BaO)/(Na₂0+K₂0+AI₂0₃) 0.50 0.64 0.52 0.39

Surface Tension(10^"3 N/m)

Heat Conductivity W/(mK)

Tg (°C) 599 577 608 616

CTE (ppm/K) 7.13 7.10 6.70 7.50

A (°C) 704 665 713 728

CS ( MPa ) 608 660 685

Dol (ym) 29 22 22

Example Example Example Exarnpl

Constituent 40 41 42 43 mol% mol% mol% mol%

Si0₂ 64.85 64.84 62.90 63.90

Al₂0₃ 12.25 12.25 14.18 15.18

Na₂0 10.02 10.02 8.02 8.02

K₂0 0.11 0.11 2.11 3.11

MgO 4.07 4.07 4.23 5.23

Zr0₂ 0.00 0.00 0.00 0.00

Ce0₂ 0.04 0.04 0.04 0.04

Sn0₂ 0.17 0.17 0.12 0.12

B₂0₃ 8.50 8.50 8.40 4.40

CaO 0.00 0.00 0.00 0.00

BaO 0.00 0.00 0.00 0.00

Na₂0+K₂0 10.13 10.13 10.13 11.13

(MgO+CaO+SrO+BaO)/(Na₂0+K₂0) 0.40 0.40 0.42 0.47

(Si02+B₂0₃+AI₂0₃)/(Na₂0+K₂0) 8.45 8.45 8.44 7.50

(AI₂0₃+CaO+MgO+SrO+BaO)/(B₂0₃+K₂0+Na₂0) 0.88 0.88 0.99 1.31

∑0/∑(Si+AI+B) 1.94 1.94 1.92 1.97

(B₂0₃+MgO+CaO+SrO+BaO)/(Na₂0+K₂0+AI₂0₃) 0.56 0.56 0.52 0.37

Surface Tension(10^"3 N/m) 322 331 308

Heat Conductivity W/(mK) 1.40 1.16 1.12

Tg (°C) 612 614 622 661

CTE (ppm/K) 6.13 5.99 6.45 6.70

A (°C) 709 717 721 750

CS ( MPa ) 698 754 621 624

Dol (ym) 19 17 23 27

Example Example Example Exarnpl

Constituent 44 45 46 47 mol% mol% mol% mol%

Si0₂ 62.90 62.92 62.90 68.00

Al₂0₃ 13.18 13.18 14.18 12.25

Na₂0 7.02 7.02 8.02 6.43

K₂0 3.11 3.11 3.11 0.11

MgO 5.23 5.23 6.23 4.00

Zr0₂ 0.00 0.00 0.00 0.00

Ce0₂ 0.04 0.00 0.04 0.04

Sn0₂ 0.12 0.12 0.12 0.17

B₂0₃ 8.40 8.41 5.40 9.00

CaO 0.00 0.00 0.00 0.00

BaO 0.00 0.00 0.00 0.00

Na₂0+K₂0 10.13 10.13 11.13 6.54

(MgO+CaO+SrO+BaO)/(Na₂0+K₂0) 0.52 0.52 0.56 0.61

(Si0₂+B₂0₃+AI₂0₃)/(Na₂0+K₂0) 8.34 8.34 7.41 13.65

(AI₂0₃+CaO+MgO+SrO+BaO)/(B₂0₃+K₂0+Na₂0) 0.99 0.99 1.23 1.05

∑0/∑(Si+AI+B) 1.94 1.94 1.98 1.90

(B₂0₃+MgO+CaO+SrO+BaO)/(Na₂0+K₂0+AI₂0₃) 0.58 0.59 0.46 0.69

Surface Tension(10^"3 N/m) 339 330 290

Heat Conductivity W/(mK) 1.14 1.16 1.12

Tg (°C) 616 615 614 653

CTE (ppm/K) 5.80 6.38 6.34 4.64

A (°C) 718 707 720 750

CS ( MPa ) 527 508 673

Dol (ym) 22 25 27

Claims

What is claimed is

A boron aluminosilicate glass article for manufacturing a chemically toughened glass article, preferably a housing or cover of an electronic device or a mobile electronic device, wherein the glass composition of the glass article is substantially free of Lithium, and wherein the glass composition comprises:

Si0₂ from 40 mol % to 75 mol %;

A1₂0₃ from 8 mol % to 20 mol %;

Na₂0+K₂0 from 0.1 mol % to 20 mol %;

MgO+CaO+BaO+SrO from 0 mol % to 8 mol %;

Zr0₂ from 0 mol % to 5 mol %;

B₂0₃ from 1 mol % to 30 mol %;

Ce0₂ from 0 mol % to 1 mol %,

wherein the ratio of R'0/R₂0 is equal or less than 0.7, preferably equal or less than 0.65 and more preferably equal or less than 0.6, R'O being the sum of MgO, CaO, SrO and BaO and R₂0 being the sum of Na₂0 and K₂0, and wherein R₂0 > 0 and R'O >= 0.

A boron aluminosilicate glass article as claimed in claim 1, wherein the average coefficient of thermal expansion (CTE) at a temperature of 20 to 300°C of the glass article is less than 7.5 ppm/K , preferably equal or less than 7.2 ppm/K , and more preferably equal or less than 7.0 ppm/K.

A boron aluminosilicate glass article as claimed in any of the preceding claims, wherein the average coefficient of thermal expansion (CTE) at a temperature of 20 to 300°C of the glass is equal or more than 3.0 ppm/K, preferably equal or more than 3.5 ppm/K , and more preferably equal or more than 4.0 ppm/K.

A boron aluminosilicate glass article as claimed in any of the preceding claims, wherein the ratio of

(Si0₂+B₂03+Al203) / (Na₂0+K₂0) is from 5 to 23, preferably from 6 to 17 and more preferably from 7 to 15.

(Al₂0₃+CaO+MgO+SrO+BaO) / (B₂0₃+K₂0+Na₂0) is from 0.1 to 1.8, preferably from 0.3 to 1.6 and more preferably from 0.4 to 1.5.

A boron aluminosilicate glass article as claimed in any of the preceding claims, wherein the ratio of ΣΟ/Σ (Si+Al+B) is from 1.0 to 2.5, preferably from 1.3 to 2.3 and more preferably from 1.5 to 2.

(B₂0₃+MgO+CaO+SrO+BaO) / (Na₂0+K₂0+Al₂0₃) is from 0 to 3.3, preferably from 0.1 to 3.1 and more preferably from 0.2 to 2.9.

A boron aluminosilicate glass article as claimed in any of the preceding claims, wherein the content of R₂0 is equal or more than 4 mol %, preferably equal or more than 6 mol % and more preferably equal or more than 8 mol % and wherein R₂0 is at least one of Na₂0 and K₂0.

9. A boron aluminosilicate glass article as claimed in any of the preceding claims, wherein the glass article is chemically toughened by ion exchange having a depth of layer (Dol) that is equal or more than 8 ym, preferably equal or more than 10 ym and more preferably equal or more than 15 ym.

10. A boron aluminosilicate glass article as claimed any of the preceding claims, wherein the glass article having a compressive stress (CS) equal or more than 450 MPa, preferably equal or more than 500 MPa and more preferably equal or more than 550 MPa.

11. A boron aluminosilicate glass article as claimed any of the preceding claims, wherein the glass article having a heat conductivity λ equal or more than 0.9 W/ (mK) , preferably equal or more than 1.0 W / (mK) and more preferably equal or more than 1.1 W/ (mK) . 12. A boron aluminosilicate glass article as claimed any of the preceding claims, wherein the glass article having a glass transition temperature T_g of equal or more than 550 ^°C, preferably equal or more than 570°C and more preferably equal or more than 580°C.

13. A boron aluminosilicate glass article as claimed any of the preceding claims, wherein the glass article having a thermal shock resistance ΔΤ equal or more than 450 ^°C, preferably equal or more than 500 °C and more preferably equal or more than 640°C.

14. A boron aluminosilicate glass article as claimed any of the preceding claims, wherein the glass article having a high surface tension o, which is defined as the molecule interaction on the surface of molten glass liquid, and wherein σ is equal or more than 200 * 10^~3 N/m, preferably equal or more than 210 * 10^~3 N/m and preferably equal or more than 220 * 10^~3 N/m at melting temperature.

15. A boron aluminosilicate glass article as claimed in any of the preceding claims, wherein the compressive stress (CS) can be improved by 10%, preferably by 20% and more preferably by 30%, and wherein the chemical toughening time can be shorten by 10%, preferably by 20% and more preferably by 30%, by the usage of doped ion Cs+ in KNO3 by only one step of ion exchange.

16. A boron aluminosilicate glass article as claimed in any of the preceding claims, wherein the glass article comprises thin glass or ultrathin glass having a thickness of about equal or less than 1.0 mm, equal or less than 0.5 mm, equal or less than 0.3 mm, equal or less than 0.1 mm, equal or less than 0.05 mm, equal or less than 0.03 mm.

17. A boron aluminosilicate glass article as claimed in any of the preceding claims, wherein the glass article comprises thin glass or ultrathin glass that can be formed by float, micro-float, down-draw slot-draw, or

fusion-draw .

18. A boron aluminosilicate glass article as claimed in any of the preceding claims, wherein the glass article comprises thin glass or ultrathin glass that can be processed by mechanical cutting with a diamond tip or a cutting wheel or an alloy cutting wheel, or that can be cut by thermal cutting or laser cutting, or that can be processed by hole drilling using ultrasonic drilling or sand blasting, or that can be chemically etched on the edge or surface to make structures.

19. A boron aluminosilicate glass article as claimed in any of the preceding claims , wherein the method of laser cutting includes conventional CW laser cutting and nonconventional filament cutting with a ultra-short pulse laser .

20. A boron aluminosilicate glass article as claimed in any of the preceding claims, wherein the chemically toughened glass article can be used on one glass solution and can be processed by laser cutting or mechanical cutting .

21. A boron aluminosilicate glass article as claimed in any of the preceding claims, wherein the glass article can be laminated with sapphire directly, or with glass powder or with optical clear adhesive (OCA) , and wherein the glass article can be used as cover glass of an electronic device such as a watch, a cellphone, a touchpad, a GPS-system and the like.

22. A boron aluminosilicate glass article as claimed in any of the preceding claims, wherein the refractive index of the glass article can be adjusted by ion exchange to match the refractive index of sapphire which is used to improve lighting output efficiency of the application.

23. A boron aluminosilicate glass article as claimed in any of the preceding claims, wherein one or more metal with high molecular refractive index is used containing dopant sources that comprises one or more of Ag, K, Cs, Ba, Y, La, Bi, Pr, Te, Ge, Ti, Zr, Nb, Ta, W, Mn,Er, Yb, Lu, and wherein the refractive index n_d is equal to or more than 1.52, preferably equal to or more than 1.53, and more preferably equal to or more than 1.54. 24. A boron aluminosilicate glass article as claimed in any of the preceding claims, wherein the glass article can be colorized by ion exchanging accompanied with chemical toughening and wherein one or more metal is used containing a dopant source that comprises one or more of Au, Ag, Cu, Ni, Co, Fe, Mn, Cr, V, Ti, La, Ce, Pr, Nd, Sm,

Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu .

25. A boron aluminosilicate glass article as claimed in any of the preceding claims, wherein the glass article can be crystallized on the surface by ion exchange in order to improve glass strength, hardness and scratch resistance .

26. A boron aluminosilicate glass article as claimed in any of the preceding claims, wherein the glass article can be doped antimicrobial by Ag+, Cu+ in KNO3 within one step of chemical toughening, and wherein the glass article can be used as cover glass of electronic devices such as a watch, a cellphone, a touchpad, a GPS-system, an ATM or for a visual display-system in hospital and the like.

27. A boron aluminosilicate glass article as claimed in the preceding claim, wherein the glass article can be formed to a 3D- or a 2.5D-shape by precision molding. 28. A boron aluminosilicate glass article as claimed in any of the preceding claims, comprising the following glass composition and conditions:

A method to manufacture a boron aluminosilicate glass article as claimed in any of the preceding claims, wherein the glass article is pre-heated at a temperature of 300 to 400°C and the time of pre-heating can be limited to 30 minutes, 20 minutes, 10 minutes or 5 minutes, wherein the glass article is then chemically toughened in molten salt,

wherein the chemical toughening temperature is from 350 to 490°C,

wherein the chemical toughening time is in a range of about

1 to 16 hours,

and wherein a post-annealing of the glass article is performed at a temperature from 300 to 400 °C and the time of post-annealing can be limited to 30 minutes, 20 minutes, 10 minutes, 5 minutes.

30. A method to manufacture a boron aluminosilicate glass article as claimed in any of the preceding claims, wherein the chemical toughening temperature is from 400 to 480 °C and wherein the chemical toughening time is from

2 to 8 hours .

31. The usage of a a boro-aluminosilicate glass article as claimed in any of the preceding claims that is chemically toughened, for cellphones, smart phones, tablet PC, notebooks, PDA, cover for non mobile devices (TV, PC, ATM machines, industrial displays) , used for flexible cover on folding screening display, OLED, used for cover for touch displays, used for protection windows, automotive windows, train windows, aviation,

harddisksubstrate, high temperature instrument panel or solar cell substrate, or used for white goods, including refrigerator or cooking tool.