Patent Application
20180155238
This application claims priority from and the benefit of Korean Patent Application No. 10-2016-0163702, filed on Dec. 2, 2016, which is hereby incorporated by reference for all purposes as if fully set forth herein.
The invention relates generally to flexible glass articles, more specifically, to a flexible glass article having a low bending curvature and a method of making the same.
Recently there has been increased need for glass articles to be flexible for use in a variety of applications that require the glass to be flexible and bendable. For example, flexible display devices for mobile phones, tablets and other portable electronic devices include flexible glass that must be bendable or foldable without breaking. However, glass had been traditionally considered rigid in nature, and therefore alternative materials have been considered for use instead of glass. For example, flexible films made of polymer have been considered and researched for use in flexible display devices as an alternative for glass. The flexible film indeed provided necessary flexibility, but did not meet the necessary durability, resistance to scratch, chemical resistance, and optical characteristics for such applications.
Chemically strengthened glass panels also have been considered for use as flexible glass, but the chemically strengthened glass panels showed relatively large bending radii of greater than 20 mm. For example, when using glass chemically strengthened to have increased surface compression, in order for the chemically strengthened glass to have a bending radius of 1 mm, the thickness of the glass would have to be about 5 μm, and to have a bending radius of 3 mm, the thickness the glass would have to be about 40 μm.
However, it is practically impossible to reduce the thickness of a glass panel to less than 25 μm using glass etching, which is conventionally used to reduce thickness of glass from between 400 μm and 700 μm to less than 100 μm, because of lack of uniformity.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the inventive concepts, and, therefore, it may contain information that does not form the prior art that is already known to a person of ordinary skill in the art.
Flexible glass articles constructed according to the principles of the invention and methods of making the same avoid one or more of the problems and/or drawbacks of conventional glass articles by providing an ultra-low bending curvature, while still retaining a thin profile and other favorable characteristics of glass.
Additional aspects will be set forth in the detailed description which follows, and, in part, will be apparent from the disclosure, or may be learned by practice of the inventive concepts.
According to an exemplary embodiment, a flexible glass article may include: a glass element having a first thickness of about 25 μm to about 100 μm and including first and second opposed surfaces, and a compressive stress region extending from the first surface of the glass element to a first depth in the glass element, the compressive stress region having a compressive stress of at least about 300 MPa at the first surface of the glass element; and a coating formed on the second surface of the glass element, the coating having a second thickness substantially equal to or greater than three times the first thickness, wherein the glass article may be characterized by: an absence of fracture when the glass element is bent with the first surface disposed toward the inside of the bend and held at a bend radius of about 1 mm to about 10 mm for at least 60 minutes at about 25° C. and about 50% relative humidity.
The coating included in the flexible glass article may have an elastic modulus equal to or less then 10 GPa.
The glass article of the flexible glass article may further characterized by: an absence of fracture when the glass is bent over approximately 200,000 cycles.
The second thickness may be equal to or less than 300 μm.
The coating may include a polymer.
The polymer may include at least one material selected from the group consisting of polyester acrylate and polyimide.
The glass article may be further characterized by: an impact resistance against a drop from a height of about 3 cm of a pen having a weight of about 5.8 g and a tip diameter of about 0.7 mm.
The glass article may be further characterized by: a change of yellow index equal to or less than about 2% after the glass article is exposed to a ultraviolet light having wavelength substantially between about 280 and about 360 nm for approximately 72 hours.
The compressive stress of the compressive stress region of the glass element may be substantially from about 300 MPa to about 1000 MPa.
The first depth may be at least about 1 μm.
The flexible glass article may have percentage haze substantially equal to or less than about 1.0%.
The coating may be formed directly on the second surface of the glass element.
A flexible display device may include the above glass article.
The glass article may be incorporated in a mobile phone, tablet, laptop, watch or other portable electronic device.
According to an exemplary embodiment, a method of manufacturing a flexible glass article may include the steps of: preparing a glass element having a first thickness and having first and second surfaces; chemically strengthening the glass element to form a compressive stress region extending from the first surface of the glass element to a first depth in the glass element, the compressive stress region having a compressive stress of at least about 300 MPa at the first surface of the glass element; and forming a coating on the second surface of the glass element, the coating having a second thickness substantially equal to or greater than three times the first thickness, wherein the glass article may be characterized by: an absence of fracture when the glass element is bent with the first surface disposed toward the inside of the bend and held at a bend radius of about 1 mm to about 10 mm for at least 60 minutes at about 25° C. and about 50% relative humidity.
The step of forming the coating may include: applying a coating solution on the second surface of the glass element; applying a soft mold on the coating solution; forming the coating by exposing the glass element to ultraviolet radiation to cure the coating solution; and removing the soft mold.
The step of forming the coating may further include: exposing the coating to ultraviolet radiation after removing the soft mold.
The coating solution may include at least one material selected from the group consisting of Poly(methyl methacrylate) PMMA, Polyethylene terephthalate PET, Cellulose triacetate TAC, Polyether sulfone PES, Ethylene tetrafluoroethylene ETFE, Fluorinated ethylene propylene FEP, Perfluoroalkoxy alkane PFA, organic polymer ORGA, Polycarbonate PC, Fiber-reinforced plastic FRP, Polyurethane, Polyester, Polyaramid, Polypropylene PP, Polyethylene naphthalate PEN, and Polyimide.
The step of chemically strengthening the glass element may include: exchanging sodium ion (Na+) in the glass element with potassium ion (K+) through a Na—K ion exchange reaction.
The step of chemically strengthening the glass element may further include: submerging the glass element in potassium nitride (KNO3) bath.
According to an exemplary embodiment, a method of adjusting an effective bending radius of a glass article subject to bending stress to fold the glass article from a natural bending radius of about 2.5 mm to 10 mm to a modified bending radius of about 1 mm to 5 mm may include the steps of: providing a glass element having first and a second opposed surfaces and first thickness in the range of about 25 μm to about 100 μm; chemically strengthening the glass element to form a compressive stress region extending from the first surface of the glass element to a first depth in the glass element, and forming a coating integrally on the second surface of the glass element, the coating having a second thickness substantially equal to or greater than three times the first thickness.
The step of forming the coating may include: applying a coating solution on the second surface of the glass element; applying a soft mold on the coating solution; forming the coating by exposing the glass element to ultraviolet radiation to cure the coating solution; and removing the soft mold.
The step of chemically strengthening the glass element may include: submerging the glass in potassium nitride (KNO3) bath; and exchanging sodium ion (Na+) in the glass element with potassium ion (K+) through Na—K ion exchange reaction.
The step of chemically strengthening the glass element may include forming the compressive stress region to have a compressive stress of at least about 300 MPa at the first surface of the glass element.
The glass article may be characterized by an absence of fracture when the glass element is bent with the first surface disposed toward the inside of the bend and held at a bend radius of about 1 mm to about 10 mm for at least 60 minutes at about 25° C. and about 50% relative humidity.
A neutral axis of the glass article may be shifted toward the coating in response to an increase in the second thickness of the coating, wherein the neutral axis of the glass article has zero tensile when the glass article is bent.
The foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the claimed subject matter.
The accompanying drawings, which are included to provide a further understanding of the inventive concept, and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the inventive concept, and, together with the description, serve to explain principles of the inventive concept.
In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of various exemplary embodiments. It is apparent, however, that various exemplary embodiments may be practiced without these specific details or with one or more equivalent arrangements. In other instances, well-known structures and devices are shown in block diagram form in order to avoid unnecessarily obscuring various exemplary embodiments.
In the accompanying figures, the size and relative sizes of layers, films, panels, regions, etc., may be exaggerated for clarity and descriptive purposes. Also, like reference numerals denote like elements.
When an element or layer is referred to as being “on,” “connected to,” or “coupled to” another element or layer, it may be directly on, connected to, or coupled to the other element or layer or intervening elements or layers may be present. When, however, an element or layer is referred to as being “directly on,” “directly connected to,” or “directly coupled to” is another element or layer, there are no intervening elements or layers present. For the purposes of this disclosure, “at least one of X, Y, and Z” and “at least one selected from the group consisting of X, Y, and Z” may be construed as X only, Y only, Z only, or any combination of two or more of X, Y, and Z, such as, for instance, XYZ, XYY, YZ, and ZZ. Like numbers refer to like elements throughout. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.
Although the terms first, second, etc. may be used herein to describe various elements, components, regions, layers, and/or sections, these elements, components, regions, layers, and/or sections should not be limited by these terms. These terms are used to distinguish one element, component, region, layer, and/or section from another element, component, region, layer, and/or section. Thus, a first element, component, region, layer, and/or section discussed below could be termed a second element, component, region, layer, and/or section without departing from the teachings of the present disclosure.
Spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper,” and the like, may be used herein for descriptive purposes, and, thereby, to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the drawings. Spatially relative terms are intended to encompass different orientations of an apparatus in use, operation, and/or manufacture in addition to the orientation depicted in the drawings. For example, if the apparatus in the drawings is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the exemplary term “below” can encompass both an orientation of above and below. Furthermore, the apparatus may be otherwise oriented (e.g., rotated 90 degrees or at other orientations), and, as such, the spatially relative descriptors used herein interpreted accordingly.
The terminology used herein is for the purpose of describing particular embodiments and is not intended to be limiting. As used herein, the singular forms, “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. Moreover, the terms “comprises,” “comprising,” “includes,” and/or “including,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, components, and/or groups thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
Various exemplary embodiments are described herein with reference to sectional illustrations that are schematic illustrations of idealized exemplary embodiments and/or intermediate structures. As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, exemplary embodiments disclosed herein should not be construed as limited to the particular illustrated shapes of regions, but are to include deviations in shapes that result from, for instance, manufacturing. Thus, the regions illustrated in the drawings are schematic in nature and their shapes are not intended to illustrate the actual shape of a region of a device and are not intended to be limiting.
Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure is a part. Terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense, unless expressly so defined herein.
The glass element 100, under conditions of static bent status or dynamic bending status, follows fracture mechanics of brittle material. Similar to other brittle materials, glass shows greater fracture toughness against compressive stress than tensile stress, and failure generally occurs when tensile stress is applied to the glass. Following are descriptions of the two circumstances glass fails under stress.
First is failure directly from an application of stress. The glass will break in response to the application of the stress when the stress intensity factor (K1), which represents the stress applied to flaws embedded within the glass, is greater than the fracture toughness (KIC), which may be between 0.65 MPa·m0.5 and 0.82 MPa·m0.5 for glass, from cracks propagating in a very high speed. Such failure occurs according to the following formula (1):
K1=Yσ√{square root over (πa)} Formula (1)
Wherein K1 is the stress intensity factor, Y is a geometry factor of the flaw, σ is the applied stress, and a stands for the size of the flaw.
On the other hand, a fatigue fracture of the glass under static stress occurs differently. Under static stress, sizes of the flaws embedded in the glass slowly grow according is to environmental factors, such as relative humidity, resulting in propagation of cracks and the failure of the glass. The speed of the flaw size growth is proportional to the stress intensity factor and the relative humidity.
v=v
0(K1/Klc)n Formula (2)
Wherein v is the crack velocity, v0 is an initial crack velocity, and n is the slow crack growth rate.
The most important factor in deciding whether the crack may grow is a threshold stress intensity factor (Kth), which may be between 0.2-0.27 MPa·m0.5, corresponding to the 0 region of the graph of
According to the formulas (1) and (2), the following two different approach may be taken to reduce or prevent the failure of glass in bent status under static and/or dynamic stress: 1) a flawless processing to reduce the size of the flaw imbedded in the glass generated during cutting, chamfering, and treating of the glass; and 2) maintaining the stress intensity under the condition that the fracture or breakage and/or fatigue fracture may not occur by the bending of the glass.
Wherein σ is the tensile stress, E is Young's Modulus, t is the thickness of the glass, v is the Poisson rate, and D is the distance between the 2 Point Bending (2PB) plates 310.
The increased compressive stress formed in the compressive stress region may reduce the actual tensile stress applied at the vertex of the parabolic shape according to following formula (4), and therefore, the formula (1) may be rewritten to formula (5):
σactual=σa−CSflaw Formula (4)
K
1
=Y (σa−CSflaw)√{square root over (π×a)} Formula (5)
Wherein σactual is the actual tensile stress, σa is the applied stress, and CSflaw is compressive stress applied at the flaw.
First, an example of the chemically strengthened glass is described when used without the coating 200. To make the chemically strengthened glass having a thickness of 50 μm, and Young's Modulus of 69.3 GPa to have a bend radius of 3 mm (R3), considering a module layer thickness of 300 μm, the chemically strengthened glass needs to be bent until the distance between the 2PB plates 310 is 5.4 mm. According to the formula (3), the applied tensile stress may be 776 MPa. If the glass is chemically strengthened to have the surface compressive stress of 850 MPa, a depth of the compressive stress region (DOL) of 10 μm, in order to prevent the fracture or breakage and/or fatigue fracture, the size of the flaw must be maintained between about 17 nm and 1.7 μm. However, it is practically impossible to use a conventional chemical flaw healing method to control the size of the flaw under 1 μm.
Referring to
Referring to
Referring to
wherein
According to the formula (6), an exemplary coating having a Young's modulus of 2 GPa and 5 GPa and a thickness between about 10 μm and about 300 μm formed onto the glass element 100 having a thickness between about 20 μm and about 40 μm. Since the thickness of the coating is inversely proportional to an effective thickness, the bending radius may be reduced as the thickness of the coating 200 is increased. Following Table 1 shows the effective thickness of the glass article 10 based upon the thickness of the coating 200 and the thickness of the glass element 100:
Accordingly, following Table 2 shows the thickness of the coating 200 necessary to make the effective thickness of the glass article 10 to be about 5 μm:
Particularly, the glass article 10 having the glass element 100 with a thickness of 30 μm and the coating 200 having a Young's modulus of 5 GPa and a thickness of 155 μm, when bent, may have the effective thickness of 4.88 μm. Thus, the glass article 10 may have the same bending characteristics as the glass having a thickness of 5 μm, which may have a bending radius of 1 mm, and therefore, the glass article 10 may have the effective bending radius of 1 mm (R1).
Referring to
For example, forming the coating 200 directly onto the glass element 100 may include following steps:
First, while
The glass element may be chemically strengthening to form a compressive stress region extending from the first surface of the glass element to a first depth in the glass element, with the compressive stress region preferably having a compressive stress of at least about 300 MPa at the first surface of the glass element 520. Various methods may be used to chemically strengthen the glass element. For example, the glass element may be chemically strengthened by exchanging sodium ions (Na+) in the glass element with potassium ions (K+) through a Na—K ion exchange reaction. By exchanging the potassium ions (K+), which has relatively bigger size that that of the sodium ion (Na+), the surface compressive stress may be increased in the surface of the glass element. For example, the Na—K ion exchange reaction may be performed by submerged the glass element in potassium nitride (KNO3) bath.
After the glass element is chemically strengthened, a coating may be formed on the second surface of the glass element, wherein the coating preferably has a second thickness substantially equal to or greater than three times the first thickness 530. Various methods may be used to form the coating directly on the glass element. For example, forming the coating is directly on the glass element may include: applying a coating solution on the second surface of the glass element; applying a soft mold on the coating solution; forming the coating by exposing the glass element to ultraviolet radiation to cure the coating solution; and removing the soft mold. The coating 200 becomes a part of the glass article, and therefore, the coating 200 has relatively high optical transmittance and resistance to heat. Also, the material may be cured by ultraviolet radiation, but the material should not turn yellow by ultraviolet radiation and should not have haze when cured.
For example, the coating solution may include at least one of Poly(methyl methacrylate) PMMA, Polyethylene terephthalate PET, Cellulose triacetate TAC, Polyether sulfone PES, Ethylene tetrafluoroethylene ETFE, Fluorinated ethylene propylene FEP, Perfluoroalkoxy alkane PFA, organic polymer ORGA, Polycarbonate PC, Fiber-reinforced plastic FRP, Polyurethane, Polyester, Polyaramid, Polypropylene PP, Polyethylene naphthalate PEN, and Polyimide.
Furthermore, the coating may be exposed to ultraviolet radiation again after removing the soft mold to further cure the coating 200.
Referring to
Referring to
On the other hand, the glass article 10 according to the exemplary embodiments having the glass element 100 with greater thickness may have relatively small bending radius. Following Table 3 is the calculation of the effective thickness of the glass article 10 including the glass element 100 having a thickness of about 25 μm, based upon the thickness and the Young's modulus of the coating 200, according to the exemplary embodiments.
According to the Table 3, the neutral axis of the glass article 10 may be shifted into the coating 200, and therefore, 0 tensile stress may be applied to the glass article 10 when the glass article 10 is bent with the first surface of the glass article 10 disposed toward the inside of the bend. For example, to shift the neutral axis of the glass article 10 into the coating 200, the coating 200 having a Young's modulus of about 1 GPa may have a thickness of at least 8.4 times the thickness of the glass element 100 (=210/25), and the coating 200 having a Young's modulus of about 10 GPa may have a thickness of at least 2.8 times the thickness of the glass element 100 (=70/25). More particularly, the coating 200 including polyimide, which has relatively large Young's modulus of about 6 GPa, may have a thickness of 3.6 times the thickness of the glass element 100.
Therefore, the coating 200 may have a thickness of at least 3 times the thickness of glass element 100. Following Table 4 shows various test results comparing (a) conventional chemically strengthened glass element used individually and (b) the glass article according to the exemplary embodiments. Both the conventional chemically strengthened glass element and the chemically strengthened glass element 100 included in the glass article 10 have a thickness of 30 μm, and a compressive stress region having a compressive strength of about 600 MPa and the depth (DOL) of about 6 μm. The glass article according to the exemplary embodiments may include a coating 200 having a thickness of 240 μm and a Young's modulus of about 2.0 GPa.
According to the test results, the individual glass element failed to pass the 1 mm bending test at the first bending. On the other hand, the glass article according to the exemplary embodiments passed the 200K dynamic bending test and the static bending test of 600 minutes. Both the individual glass element and the glass article according to the exemplary embodiments have substantially the same optical characteristics.
The shock resistance test may be performed by dropping pen on to test subject. The test subject may be attached to a base film using a pressure sensitive adhesive having a thickness of 50 μm and Young's modulus of about 1 MPa. The base film may be attached to a steel plate. The base film may include Polyethylene terephthalate PET having a thickness of 50 μm. The pen used in the test is BIC® ORANGE™ FINE pen, having a point diameter of 0.7 mm and weight of 5.8 g. The drop test is performed by increasing the drop height by 1 cm after the test subject passes the test until the test subject fails. According to the test results, the individual is glass element broke at a 1 cm drop, and the glass article according to the exemplary embodiment broke at a 3 cm drop.
Referring to
Referring to
Referring to
Although certain exemplary embodiments and implementations have been described herein, other embodiments and modifications will be apparent from this description. Accordingly, the inventive concept is not limited to such embodiments, but rather to the broader scope of the presented claims and various obvious modifications and equivalent arrangements.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2016-0163702 | Dec 2016 | KR | national |
