# US 9,434,633 B2 · Glass sheets with improved mechanical strength

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- Number: US 9,434,633 B2
- Document ID: US9434633B2
- Status: Granted
- Kind: B2
- Application number: 13/170,675
- Filed: 2011-06-28
- Published: 2011-12-29
- Granted: 2016-09-06
- Earliest claimed: 2010-06-29
- Assignees: Corning Incorporated
- Applicants: Dana Craig Bookbinder; Keith Leonard House; Pushkar Tandon
- Inventors: Dana Craig Bookbinder; Keith Leonard House; Pushkar Tandon
- Web page: https://patentgrep.com/patent/US9434633B2

## CPC

- C03B 17/02: Forming {molten} glass coated with coloured layers; {Forming molten glass of different compositions or layers; Forming molten glass comprising reinforcements or inserts}
- C03B 17/064: {by the overflow downdraw fusion process; Isopipes therefor}
- C03B 17/068: {Means for providing the drawing force, e.g. traction or draw rollers}
- C03C 3/083: containing aluminium oxide or an iron compound
- C03C 3/085: containing an oxide of a divalent metal
- C03C 3/087: containing calcium oxide, e.g. common sheet or container glass
- C03C 3/091: containing aluminium
- C03C 3/093: containing zinc or zirconium
- Y10T 428/2495: Thickness [relative or absolute]
- C03B: MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03C: CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
- Y10T: TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION

## Abstract

Transparent glass sheets having increased mechanical strength include an inner layer surrounded by surface compressive layers wherein the difference of the coefficient of thermal expansion of the inner layer and the surface compressive layer is greater than 50×10−7° C.−1 and wherein the surface compressive layer has a compressive stress of at least about 300 MPa.

## Claims

### Claim 1

A transparent glass sheet comprising a surface compressive layer and an inner layer adjacent to the surface compressive layer,
wherein between 0° C. and 300° C. a difference between a coefficient of thermal expansion of the inner layer and a coefficient of thermal expansion of the surface compressive layer is greater than 50×10−7° C.−1, and
wherein the surface compressive layer has a compressive stress of at least about 300 MPa and the inner layer has a tensile stress of at least 29 MPa.

### Claim 2 (depends on 1)

The transparent glass sheet according to claim 1, wherein between 0° C. and 300° C. a ratio of the coefficient of thermal expansion of the inner layer to the coefficient of thermal expansion of the surface compressive layer is greater than 2.5.

### Claim 3 (depends on 1)

The transparent glass sheet according to claim 1, wherein the transparent glass sheet has a thickness and the inner layer has a thickness, and a ratio of the thickness of the inner layer to the thickness of the transparent glass sheet is at least about 0.8.

### Claim 4 (depends on 1)

The transparent glass sheet according to claim 1, wherein the transparent glass sheet has a thickness ranging from about 0.3 mm to about 3 mm.

### Claim 5 (depends on 1)

The transparent glass sheet according to claim 1, wherein the softening point of the surface compressive layer is at least 40° C. below a softening point of the inner layer.

### Claim 6 (depends on 1)

The transparent glass sheet according to claim 1, wherein the ratio of the viscosity of the surface compressive layer to a viscosity of the inner layer in a range of the softening point of the inner layer ±200° C. is from about 0.1 to about 0.9.

### Claim 7 (depends on 1)

The transparent glass sheet according to claim 1, wherein the inner layer comprises in weight percent on an oxide basis: (i) 50≦SiO2≦65%; (ii) 10≦Al2O3≦20%; (iii) 0≦MgO≦5%; (iv) 10≦Na2O≦20%; (iv) 0≦K2O≦5%; and (v)≧0 and ≦1% of at least one of B2O3, CaO, ZrO2 and Fe2O3.

### Claim 8 (depends on 1)

The transparent glass sheet according to claim 1, wherein the surface compressive layer has a compressive stress of at least about 500 MPa.

### Claim 9 (depends on 1)

The transparent glass sheet according to claim 1, wherein no layer of the transparent glass sheet has been subjected to an in situ crystallization process.

### Claim 10 (depends on 1)

The transparent glass sheet according to claim 1, wherein less than 10 ppm of any layer in the glass sheet is in a crystalline state.

### Claim 11 (depends on 1)

The transparent glass sheet according to claim 1, wherein no layer of the transparent glass sheet has been subjected to an ion exchange process.

### Claim 12 (depends on 1)

The transparent glass sheet according to claim 1, wherein between 0° C. and 300° C. a ratio of the coefficient of thermal expansion of the inner layer to the coefficient of thermal expansion of the surface compressive layer is greater than 3.

### Claim 13 (depends on 1)

The transparent glass sheet according to claim 1, wherein between 0° C. and 300° C. the difference of the coefficient of thermal expansion of the inner layer and the coefficient of thermal expansion of the surface compressive layer is greater than 75×10−7° C.−1.

### Claim 14 (depends on 1)

The transparent glass sheet according to claim 1, wherein the transparent glass sheet has a thickness and the inner layer has a total thickness, and a ratio of the total thickness of the inner layer to the thickness of the transparent glass sheet is at least about 0.9.

### Claim 15 (depends on 1)

The transparent glass sheet according to claim 1, wherein between 0° C. and 300° C. a ratio of the coefficient of thermal expansion of the inner layer to the coefficient of thermal expansion of the surface compressive layer is greater than 4.

### Claim 16 (depends on 1)

The transparent glass sheet according to claim 1, wherein between 0° C. and 300° C. the difference between the coefficient of thermal expansion of the inner layer and the coefficient of thermal expansion of the surface compressive layer is greater than 90×10−7° C.−1.

### Claim 17 (depends on 1)

The transparent glass sheet according to claim 1, wherein the surface compressive layer has a compressive stress of at least about 700 MPa.

### Claim 18 (depends on 1)

The transparent glass sheet according to claim 1, wherein the inner layer has a tensile stress of at least about 57 MPa.

### Claim 19 (depends on 1)

The transparent glass sheet according to claim 1, wherein the inner layer comprises an alkali aluminosilicate glass.

### Claim 20 (depends on 1)

The transparent glass sheet according to claim 1, wherein the surface compressive layer comprises in weight percent on an oxide basis: (i) 65≦SiO2≦75%; (ii) 7≦Al2O3≦13%; (iii) 5≦B2O3≦15%; (iv) 5≦CaO≦15%; (v) 0≦BaO≦5%; (vi) 0≦MgO≦3%; and (vii) 0≦SrO≦5%.

### Claim 21 (depends on 20)

The transparent glass sheet according to claim 20, wherein the surface compressive layer is essentially free of BaO.

### Claim 22 (depends on 1)

The transparent glass sheet according to claim 1, wherein a ratio of a thickness of the inner layer to a thickness of the transparent glass sheet is less than or equal to 0.9.

### Claim 23 (depends on 1)

The transparent glass sheet according to claim 1, wherein the inner layer has a tensile stress of at least about 42 MPa.

### Claim 24

A transparent glass sheet comprising a surface compressive layer and an inner layer adjacent to the surface compressive layer, wherein between 0° C. and 300° C. the difference between the coefficient of thermal expansion of the inner layer and the coefficient of thermal expansion of the surface compressive layer is greater than 50×10−7° C.−1, the surface compressive layer has a compressive stress of at least about 300 MPa, and a ratio of a thickness of the inner layer to a thickness of the transparent glass sheet is less than or equal to 0.9.