LONG-TERM BENDABLE GLASS MATERIAL, AND METHOD FOR THE PRODUCTION OF A LONG-TERM BENDABLE GLASS MATERIAL

Abstract

A method for producing long-term bendable glass material includes: bending a glass material in a bending radius in a range of 1 mm to 10.sup.7 mm; storing the bent glass material for a time period of at least 1 day; inspecting at least a portion of the bent glass material for damage after the storing; and classifying the inspected bent glass material as a reject if damage is detected or as a long-term bendable glass material if no damage is detected.

Claims

1. A method for producing long-term bendable glass material, comprising: bending a glass material in a bending radius in a range of 1 mm to 10.sup.7 mm; storing said bent glass material for a time period of at least 1 day; inspecting at least a portion of said bent glass material for damage after said storing; and classifying said inspected bent glass material as a reject if damage is detected or as a long-term bendable glass material if no damage is detected.

2. The method according to claim 1, further comprising winding said glass material onto a roll, said glass material having a maximum thickness of 500 μm and a minimum thickness of 3 μm.

3. The method according to claim 2, further comprising rewinding said wound glass material from said roll onto a second roll.

4. The method according to claim 1, wherein said glass material comprises the following components in weight-%: SiO.sub.2 40-75; Al.sub.2O.sub.3 1-25; B.sub.2O.sub.3 0-16; alkaline earth oxide 0-30; and alkali oxide 0-20.

5. The method according to claim 1, wherein said inspected glass material is a cut-off of said bent glass material.

6. The method according to claim 1, wherein said glass material comprises at least one coating.

7. The method according to claim 1, further comprising pre-treating said glass material prior to said bending.

8. The method according to claim 1, wherein said glass material is a composite material having a polymer film.

9. The method according to claim 1, wherein said glass material is stored at least one of at a relative humidity in a range between 40% and 100% and at a temperature in a range between 10° C. and 30° C.

10. A method for proof testing glass material, comprising: bending a glass material; storing said bent glass material for a period of at least 1 day; determining a crack depth in said glass material after said storing; comparing said determined crack depth with a predefined crack depth; and classifying said glass material as a long-term bendable glass material if said crack depth is less than said predetermined crack depth such that a remaining probability of breaking is less than 0.1 for a maximum storage period of half a year.

11. The method according to claim 10, further comprising defining said predetermined crack depth as ((K.sub.1c.Math.R)/(E.Math.d)).sup.2, wherein K.sub.1c is a fracture toughness of said glass material, R is a bending radius of said glass material, E is an elasticity modulus of said glass material, and d is a thickness of said glass material.

12. The method according to claim 11, wherein at least one of said fracture toughness is in a range of 0.1 to 1.5 MPa.Math.√m, said elasticity modulus is in a range of 40 to 150 GPa, and said bending radius is in a range of 1 mm to 10.sup.7 mm.

13. The method according to claim 10, wherein said glass material comprises the following components in weight-%: SiO.sub.2 40-75; Al.sub.2O.sub.3 1-25; B.sub.2O.sub.3 0-30; and alkali oxide 0-20.

14. The method according to claim 10, wherein said glass material comprises at least one coating.

15. The method according to claim 10, further comprising pre-treating said glass material prior to said bending.

16. The method according to claim 10, wherein said glass material is a composite material having a polymer film.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0088] The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:

[0089] FIG. 1 is a progression of a break development for a 50 μm thick thin glass film of glass AF32;

[0090] FIG. 2 is break progression for a 100 μm thick thin glass film of glass AF32;

[0091] FIG. 3 is a Weibull-diagram of strength (breaking stress) over the probability of failure of a reference glass sample;

[0092] FIG. 4 is a Weibull-diagram of strength (breaking stress) over the probability of failure for a glass sample with a radius of 30 mm;

[0093] FIG. 5 is a Weibull-diagram of strength (breaking stress) over the probability of failure for a glass sample with a radius of 25 mm;

[0094] FIG. 6 is a Weibull-diagram of strength (breaking stress) over the probability of failure for a glass sample with a radius of 22.5 mm;

[0095] FIG. 7 is a Weibull-diagram of strength (breaking stress) over the probability of failure for a glass sample with a radius of 20 mm;

[0096] FIG. 8 is a Weibull-diagram of strength (breaking stress) over the probability of failure for a glass sample with a radius of 17 mm;

[0097] FIG. 9 is a Weibull-diagram of strength (breaking stress) over the probability of failure for a glass sample with a radius of 15 mm; and

[0098] FIG. 10 is a Weibull-diagram of strength (breaking stress) over the probability of failure for a glass sample with a radius of 14 mm.

[0099] Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate embodiments of the invention and such exemplifications are not to be construed as limiting the scope of the invention in any manner.

DETAILED DESCRIPTION OF THE INVENTION

[0100] Referring now to the drawings, and more particularly to FIGS. 1 and 2, the probability of breakage is given over time for a multitude of glass rolls having a diameter of 85 mm, including a glass roll having a thickness of 50 μm. Intermediate layers consisting of a physically crosslinked, closed-cell polyolefin-foam, as offered under the trade name Alveolit by SEKISUI ALVEO BS GmbH/D-Bad Sobernheim is inserted between the individual glass layers. The glass rolls are enclosed in plastic covers and are stored at room temperature. The moisture was hereby variable between 20% and 85%. Overall, several observations were conducted. The total observation period was 300 days. The development of a break in a 50 μm thick thin glass film of AF32 is illustrated in FIG. 1. As can be seen, the probability of breaking strongly increases initially and remains then on a largely constant level. At best, a small increase can be detected after a certain storage time.

[0101] Rolls of thin glass ribbons with a thickness of 50 μm consisting of an alkali-free alumino-borosilicate glass were inspected as glass material. This glass AF32 by Schott AG., Mainz is a glass consisting of the following components in weight-%:

SiO.SUB.2.: 61.4;

[0102] Al.sub.2O.sub.3: 17.5;
B.sub.2O.sub.3: 10.5;
alkaline earth oxide: 10.3; and
alkali oxide: 0.

[0103] As can be seen in FIG. 1, the number of breaks strongly increases at the beginning to 4 breaks/km length of film and increases only slowly with extended storage times. After 4 weeks or 30 days, a virtually stationary state is reached and no significant increase in the number of breaks is detected. The probability of breaks after 30 days is less than 0.03, such as less than 0.01. Over several months of storage period, the glass film shows no significant increase in the number of breaks

[0104] The following applies to the tension σ in the glass roll:

[00002]$\sigma =E.Math.\frac{t}{2R}$

E=the Young's (elastic) modulus which, in the case of AF32 is 74 GPa;
t=the glass thickness which, in the case of AF32 is 50 μm; and the core diameter R of the roll=85 mm.

[0105] For the tension σ for the roll consisting of a 50 μm thick AF32 glass film this suggests a value of approximately 21 MPa for the tension in the glass roll; for a 100 μm thick glass film a tension of 45 MPa.

[0106] FIG. 2 illustrates the results for a 100 μm thick AF32 glass film. As can be seen from FIG. 2, the number of breaks also increases rapidly in this case within 25 days. In contrast to the 50 μm thick glass film, the level from which the number of breaks remains largely constant is reached only after more than 100 days. As in the case with the 50 μm thick glass film, the probability of breaking when stored longer than 150 days is 0.01, in other words 1% lower. For the tension in the glass roll, a value of σ=45 MPa is determined.

[0107] The glass rolls that are stored over at least 1 day, such as at least 5 days, at least 7 days, at least 10 days, at least 50 days, at least 150 days, or at least 300 days with low probability of breaking are categorized as remaining stable over a long-term storage period, or long-term bendable, or usable in a curved state. Such glasses find use in curved indicator devices, such as curved cover glasses or display glasses.

[0108] Surprisingly, after conducting the proof-test, i.e., classifying the glass material as long-term bendable, an increase in strength was achieved due to filleting of the crack tips.

[0109] With glass that is subjected to the proof-test, subcritical crack formation occurs due to tensile stress. This means that all cracks that reach the critical crack length, i.e., the predetermined crack length during a given time period, will result in a break. Storage in accordance with the proof-test is therefore a test during which glasses with micro-cracks that are not shorter than the critical crack length—that is the target value—are rejected. Cracks that do not lead to a break within the first short time period, will also not lead to a break after a long time period.

[0110] This makes it possible to put a greater load onto the glass roll after conducting the proof-test. It has been shown that loads can be greater of up to 20% than in the proof-test. The range of the possible load increase is therefore 0 to 20%. Values of 5%, 10%, 15% load increase are possible. As is the case in the proof-test, the load is adjusted through the winding radius. The following applies for the tensile stress:

[00003]$\sigma =E.Math.\frac{t}{2R}$

whereby:
t: is the thickness of the glass material;
R: is the winding radius; and
E: is the Young's modulus.

[0111] FIGS. 3-10 demonstrate the surprising fact that the glass becomes stronger during storage.

[0112] FIG. 3 illustrates the Weibull diagram as strengths of a reference sample.

[0113] FIGS. 4-10 illustrate the Weibull diagrams of glasses that were stored longer, after conducting the proof-test and under greater loads than during the proof-test as a comparison to a reference sample from FIG. 3. In FIG. 4, the inspected sample had a radius of 30 mm; in FIG. 5, the inspected sample had a radius of 25 mm; in FIG. 6, the inspected sample had a radius of 22.5 mm; in FIG. 7, the inspected sample had a radius of 20 mm; in FIG. 8, the inspected sample had a radius of 17 mm; in FIG. 9, the inspected sample had a radius of 15 mm; and in FIG. 10, the inspected sample had a radius of 14 mm. The glasses are maintained over a longer time period under strong tension after the proof-test was conducted.

[0114] Surprisingly, it can be appreciated from FIGS. 4-10 that the samples with high strengths become clearly worse, but the samples whose original strength is not much above the load limit are clearly better. However, if the stresses become too great, the effect is no longer easily recognizable.

[0115] With the present invention, it has been recognized for the first time how one can proceed in order to facilitate a long-term bendability for glass on a roll or in a curved application. Moreover, a proof-test is provided with which it is possible to classify long-term bendable glass samples.

[0116] While this invention has been described with respect to at least one embodiment, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.