Cover glass for display device, and manufacturing method for same

a technology for display devices and glass, applied in glass/slag layered products, chemistry apparatuses and processes, layered products, etc., can solve the problems of less likely to provide compressive stress layers at the surface portion of glass plates, failure to provide desired high strength, and easy cracking, etc., to achieve excellent mechanical strength, excellent cutting processability, and high strength.

Inactive Publication Date: 2014-08-14
CENT GLASS CO LTD
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0073]The cover glass for display devices of the present invention has excellent cutting processability, and excellent reliability of mechanical strength, that is, high strength when a cumulative fracture probability is 1%.

Problems solved by technology

A cover glass is a component that has an exposed surface, and therefore is susceptible to cracking when exposed to an impact (e.g. contact with a hard object, dropping impact).
Unfortunately, thermal strengthening, when performed on a thin glass plate, is less likely to establish a large temperature differential between the surface and the inside of the glass plate, and therefore less likely to provide a compressive stress layer at the surface portion of the glass plate.
Thus, this method fails to provide desired high strength.
Another fatal problem is that processing (e.g. cutting) of a thermally strengthened glass plate is difficult because the glass plate will shatter when a preliminary crack for cutting is formed on the surface.
However, this also causes an increase in a relaxation rate of a compressive stress derived from the viscosity of the glass.
In general, a surface compressive stress and a depth of a compressive stress layer cannot keep both the sufficient levels, and it is difficult to find production conditions suitable for chemical strengthening.
Display devices with a touch panel function explosively increase their market share.
Chemically strengthened glasses can be cut, but with great difficulty.
Cut difficulty of chemically strengthened glasses is a main reason for reducing the production yield, and also causes breakage or other problems of products made from chemically strengthened glasses.
However, this means that it does not allow even a preliminary crack for glass cutting to be formed thereon, which causes difficulty in cutting.
Even if a crack for cutting can be formed on the glass, the central tensile stress automatically propagates the crack made for cutting to cause a danger of shuttering the glass.
Thus, high strength reliability tends to impair the cutting easiness of a chemically strengthened glass.
As described above, in a chemically strengthened glass, good cutting easiness is contrary to good strength reliability.
They are therefore difficult to keep both in a balanced manner.

Method used

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  • Cover glass for display device, and manufacturing method for same
  • Cover glass for display device, and manufacturing method for same
  • Cover glass for display device, and manufacturing method for same

Examples

Experimental program
Comparison scheme
Effect test

example 1

(1) Preparation of Chemically Strengthened Glass and Evaluation of Surface Compressive Stress and Depth of Compressive Stress Layer

[0125]As a glass plate before ion exchange (chemical strengthening), a 0.7-mm thick soda-lime glass plate with 400 mm×500 mm sizes (SiO2: 71.6%, Na2O: 12.5%, K2O: 1.3%, CaO: 8.5%, MgO: 3.6%, Al2O3: 2.1%, Fe2O3: 0.10%, SO3: 0.3% (on a mass basis) the strain point of the plate glass was 503° C.) (hereinafter, referred to as glass base plate) was produced by a float process.

[0126]The glass base plate prepared above was submerged in a molten salt (first salt, proportion P: 34.7 mol %) bath composed of a mixture of 65.3 mol % of potassium nitrate and 34.7 mol % of sodium nitrate at a constant temperature of 475° C. for 120 minutes, as a first step. The glass base plate was then taken out from the bath and gradually cooled, and the surface of the glass base plate was washed and dried.

[0127]In a subsequent second step, the dried glass base plate was submerged i...

example 2

[0135]Chemically strengthened cut glasses were prepared as in Example 1 except that the thickness of the glass base plate was changed and the temperature of the first salt was set at 470° C., and evaluated. The depth of the compressive stress layer formed through the first step, the surface compressive stress, and the depth of the compressive stress layer of each glass were measured as in Example 1 to be 12 μm, 683 MPa, and 10 μm, respectively. The shape parameter and the strength when a cumulative fracture probability was 1% determined as in Example 1 were 8.07 and 512 MPa, respectively.

example 3

[0136]Chemically strengthened cut glasses were prepared as in Example 2 except that the thickness of the glass base plate was changed, and evaluated. The depth of the compressive stress layer formed through the first step, the surface compressive stress, and the depth of the compressive stress layer of each glass were measured as in Example 1 to be 12 μm, 677 MPa, and 11 μm, respectively. The shape parameter and the strength when a cumulative fracture probability was 1% determined as in Example 1 were 11.5 and 578 MPa, respectively.

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Abstract

The present invention aims to provide a cover glass for display devices, made of soda-lime glass, excellent in cutting easiness and reliability of surface strength. The cover glass for display devices of the present invention includes a chemically strengthened glass, and has a compressive stress layer having a depth of 6 to 15 μm.
In the cover glass, a shape parameter determined in accordance with JIS R 1625 (1996) based on analysis of a facture stress of the cover glass measured by a coaxial double ring test is not less than 7, and strength of the cover glass when a cumulative fracture probability is 1% is not less than 450 MPa.
The glass plate before the ion exchange is made of soda-lime glass.

Description

TECHNICAL FIELD[0001]The present invention relates to a cover glass for display devices, specifically a chemically strengthened glass suitable for cover glasses or integrated cover glasses having functions of both a substrate and a cover glass for display devices (including display devices having functions of an input arrangement) of electric devices (e.g. mobile phones, smartphones, tablet computers).BACKGROUND ART[0002]Resin covers are widely used as display protectors for mobile electronic devices such as mobile phones and smartphones. Such resin covers, however, are exceeded by those made of glass in terms of excellence in transmittance, weather resistance, and damage resistance, and additionally, glass improves the aesthetics of displays. Accordingly, there has been an increasing demand for display protectors made of glass in recent years. A cover glass is a component that has an exposed surface, and therefore is susceptible to cracking when exposed to an impact (e.g. contact w...

Claims

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Application Information

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Patent Type & Authority Applications(United States)
IPC IPC(8): C03C21/00
CPCC03C21/002
Inventor MATSUDA, YUTSUZUKI, TATSUYAMITAMURA, NAOKIMURAMOTO, TADASHI
Owner CENT GLASS CO LTD
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