This application claims priority to Korean Patent Application No. 10-2019-0171428, filed on Dec. 20, 2019, and all the benefits accruing therefrom under 35 U.S.C. 119, the content of which in its entirety is herein incorporated by reference.
The disclosure relates to a glass article and a display device including the glass article.
Glass articles are widely used in electronic devices including display devices or construction materials. More particularly, a glass article is applied to a substrate of a flat panel display device such as a liquid crystal display (“LCD”), an organic light emitting display (“OLED”) and an electrophoretic display (“EPD”), or a cover window for protecting elements covered thereby.
As portable electronic devices including glass articles, such as smart phones and tablet personal computers (“PC”s), have become more widely used, such glass articles may be frequently exposed to external impacts. Accordingly, it is desired to develop a glass article which is thin for portability and can withstand external impacts. Attempts have been made to improve the strength of a glass article by thermal or chemical strengthening but more precise stress profile management is desired to meet customer needs.
Embodiments of the disclosure provide a display device including a glass article having high strength through a precise stress profile.
An embodiment of a glass article includes a first surface; a second surface opposed to the first surface; a first compressive region extending from the first surface to a point at a first compression depth from the first surface; a second compressive region extending from the second surface to a point at a second compression depth from the second surface; and a tensile region disposed between the first compressive region and the second compressive region. In such an embodiment, a stress profile of the first compressive region includes a first segment between the first surface and a first transition point, and a second segment between the first transition point and the first compression depth, where a depth from the first surface to the first transition point is in a range of about 8.1 micrometers (μm) to about 9.5 μm, where a stress at the first transition point is greater than or equal to about 197 megapascals (MPa), and where a stress at a point of 50 μm in a depth direction from the first surface is greater than or equal to about 75 MPa.
An embodiment of a display device includes a display panel including a plurality of pixels; a cover window disposed above the display panel; and an optically transparent bonding layer disposed between the display panel and the cover window. In such an embodiment, the cover window includes: a first surface; a second surface opposed to the first surface; a first compressive region extending from the first surface to a point at a first compression depth from the first surface; a second compressive region extending from the second surface to a point at a second compression depth from the second surface; and a tensile region disposed between the first compressive region and the second compressive region. In such an embodiment, a stress profile of the first compressive region includes a first segment between the first surface and a first transition point, and a second segment located between the first transition point and the first compression depth, where a depth from the first surface to the first transition point is in a range of about 8.1 μm to about 9.5 μm, where a stress at the first transition point is greater than or equal to about 197 MPa, and where a stress at a point of about 50 μm in a depth direction from the first surface is greater than or equal to about 75 MPa.
According to embodiments of the glass article and the display device including the glass article, the glass article may have a high strength such that the glass article is not easily broken by an external impact by precisely controlling the stress profile.
The above and other features of the disclosure will become more apparent by describing in detail exemplary embodiments thereof with reference to the accompanying drawings, in which:
The invention will now be described more fully hereinafter with reference to the accompanying drawings, in which various embodiments of the invention are shown. This invention may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will filly convey the scope of the invention to those skilled in the art.
It will also be understood that when a layer is referred to as being “on” another layer or substrate, it can be directly on the other layer or substrate, or intervening layers may also be present. In contrast, when an element is referred to as being “directly on” another element, there are no intervening elements present.
It will be understood that, although the terms “first,” “second,” “third” 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 only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, “a first element,” “component,” “region,” “layer” or “section” discussed below could be termed a second element, component, region, layer or section without departing from the teachings herein.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used herein, “a”, “an,” “the,” and “at least one” do not denote a limitation of quantity, and are intended to include both the singular and plural, unless the context clearly indicates otherwise. For example, “an element” has the same meaning as “at least one element,” unless the context clearly indicates otherwise. “At least one” is not to be construed as limiting “a” or “an.” “Or” means “and/or.” As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. It will be further understood that the terms “comprises” and/or “comprising,” or “includes” and/or “including” when used in this specification, specify the presence of stated features, regions, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, components, and/or groups thereof.
Spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures 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. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.
The same reference numbers indicate the same components throughout the specification.
As used herein, the term “glass article” refers to an article made entirely or partially of glass.
“About” or “approximately” as used herein is inclusive of the stated value and means within an acceptable range of deviation for the particular value as determined by one of ordinary skill in the art, considering the measurement in question and the error associated with measurement of the particular quantity (i.e., the limitations of the measurement system). For example, “about” can mean within one or more standard deviations, or within ±30%, 20%, 10% or 5% of the stated value.
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 belongs. It will be further understood that 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 the disclosure, and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
Exemplary embodiments are described herein with reference to cross section illustrations that are schematic illustrations of idealized embodiments. 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, embodiments described herein should not be construed as limited to the particular shapes of regions as illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. For example, a region illustrated or described as flat may, typically, have rough and/or nonlinear features. Moreover, sharp angles that are illustrated may be rounded. Thus, the regions illustrated in the figures are schematic in nature and their shapes are not intended to illustrate the precise shape of a region and are not intended to limit the scope of the claims.
Hereinafter, exemplary embodiments of the disclosure will be described in detail with reference to the accompanying drawings.
A glass article may be used as a cover window for protecting a display panel, a substrate for a display panel, a substrate for a touch panel, an optical member such as a light guide plate and the like in electronic devices including a display panel, such as a tablet personal computer (“PC”), a laptop computer, a smart phone, an electronic book, a television and a PC monitor as well as a refrigerator and a cleaning machine including a display screen. A glass article may also be employed as a cover glass for a dashboard of a vehicle, a cover glass for solar cells, interior materials for construction materials, windows for buildings and houses, and the like.
Some glass articles are desired to have high strength. In one embodiment, for example, where a glass article is employed as a window, the window is desired to have a small thickness to have high transmittance and lightweight, and also have high strength such that the window is not easily broken by an external impact. Strengthened glass may be produced by, for example, chemical strengthening or thermal strengthening. Various embodiments of a strengthened glass article having various shapes are shown in
Referring to
In an exemplary embodiment, the planar shape of the glass articles 100 to 103 may be a rectangular shape, but is not limited thereto. Alternatively, the planar shape of the glass articles 100 may have one of various shapes such as a rectangular shape with rounded corners, a square shape, a circular shape, and an elliptical shape. Hereinafter, for convenience of description, exemplary embodiments where the glass articles 100 has a shape of a flat plate having a rectangular planar shape will be described in detail, but the disclosure is not limited thereto.
Referring to
In such an embodiment, the display panel 200 may include not only a self-luminous display panel such as an organic light emitting display (“OLED”) panel, an inorganic electroluminescence (“EL”) display panel, a quantum dot (“QED”) display panel, a micro light emitting display (“micro-LED”) panel, a nano light emitting display (“nano-LED”) panel, a plasma display panel (“PDP”), a field emission display (“FED”) panel and a cathode ray tube (“CRT”) display panel, but also a light receiving display panel such as a liquid crystal display (“LCD”) panel and an electrophoretic display (“EPD”) panel.
The display panel 200 includes a plurality of pixels PX and may display an image by using light emitted from each pixel PX. The display device 500 may further include a touch member (not shown). In an exemplary embodiment, the touch member may be embedded in the display panel 200. In one exemplary embodiment, for example, the touch member is directly formed on a display member of the display panel 200, such that the display panel 200 itself may perform a touch function. In an alternative exemplary embodiment, the touch member may be manufactured separately from the display panel 200 and then attached to the top surface of the display panel 200 by an optically transparent bonding layer.
The glass article 100 is disposed above the display panel 200 to protect the display panel 200. In an exemplary embodiment, the glass article 100 is larger in size than the display panel 200, such that the side surface SS (shown in
The optically transparent bonding layer 300 is disposed between the display panel 200 and the glass article 100. The optically transparent bonding layer 300 serves to fix the glass article 100 onto the display panel 200. The optically transparent bonding layer 300 may include an optically clear adhesive (“OCA”), an optically clear resin (“OCR”), or the like.
Hereinafter, the strengthened glass article 100 will be described in greater detail.
Referring to
The first surface US and the second surface RS are opposed to each other in the thickness direction. In an exemplary embodiment, where the glass article 100 serves to transmit light in the same manner as the cover window of a display, the light may be mainly incident on one of the first surface US and the second surface RS and pass through the other one.
A thickness t of the glass article 100 is defined as a distance between the first surface US and the second surface RS. The thickness t of the glass article 100 may be in a range, but is not limited to, from about 0.1 millimeter (mm) to about 2 mm. In one exemplary embodiment, for example, the thickness t of the glass article 100 may be about 0.8 mm or less. In an alternative exemplary embodiment, the thickness t of the glass article 100 may be about 0.75 mm or less. In another alternative exemplary embodiment, the thickness t of the glass article 100 may be about 0.7 mm or less. In yet another alternative exemplary embodiment, the thickness t of the glass article 100 may be about 0.6 mm or less. In yet another alternative exemplary embodiment, the thickness t of the glass article 100 may be about 0.65 mm or less. In yet another alternative exemplary embodiment, the thickness t of the glass article 100 may be about 0.5 mm or less. In yet another alternative exemplary embodiment, the thickness t of the glass article 100 may be about 0.3 mm or less. In some exemplary embodiments, the thickness t of the glass article 100 may be in a range from about 0.6 mm to about 0.8 mm or in a range from about 0.69 mm to about 0.71 mm. The glass article 100 may have a uniform thickness t, but is not limited thereto and may have a different thickness t for each region. Hereinafter, for convenience of description, exemplary embodiments where the glass article 100 has a thickness of about 0.70 mm will be described in detail, but the disclosure is not limited thereto.
The glass article 100 may be strengthened to have a predetermined stress profile therein. The strengthened glass article 100 more efficiently prevents generation of cracks, propagation of cracks, breakage and the like due to external impact than the glass article 100 before strengthening. The glass article 100 strengthened by a strengthening process may have a different stress for each region. In one exemplary embodiment, for example, compressive regions CSR1 and CSR2 to which a compressive stress is applied may be disposed in the vicinity of the surface of the glass article 100, i.e., near the first surface US and the second surface RS, and a tension region CTR to which a tensile stress is applied may be disposed inside the glass article 100. A boundary between the compressive region CSR1, CSR2 and a tensile region CTR may have a stress value of zero. The compressive stress in one compressive region CSR1, CSR2 may vary in its stress value depending on the position (i.e. depth from the surface). Also, the tensile region CTR may have a different stress value depending on the depth from the surface US, RS.
The position of the compressive region CSR1, CSR2, the stress profile in the compressive region CSR1, CSR2, the compressive energy of the compressive region CSR1, CSR2, the tensile energy of the tensile region CTR or the like in the glass article 100 has a great influence on the mechanical properties of the glass article 100 such as the surface strength, which will be described later in greater detail.
Referring to
The molding step S11 may include preparing a glass composition and molding the glass composition.
The glass composition may include at least one material selected from various compositions known in the art. In an exemplary embodiment, the glass composition may include a lithium-alumina-silicon (“LAS”) glass ceramics containing lithium aluminosilicate. In one exemplary embodiment, for example, the glass composition may contain 50 to 80 mol % of SiO2, 1 to 30 mol % of Al2O3, 0 to 5 mol % of B2O3, 0 to 4 mol % of P2O5, 3 to 20 mol % of Li2O, 0 to 20 mol % of Na2O, 0 to 10 mol % of K2O, 3 to 20 mol % of MgO, 0 to 20 mol % of CaO, 0 to 20 mol % of SrO, 0 to 15 mol % of BaO, 0 to 10 mol % of ZnO, 0 to 1 mol % of TiO2, and 0 to 8 mol % of ZrO2.
The term “the content is 0 mol %” as used herein means that it does not substantially contain the corresponding component. The term “(composition) does not substantially contain (a certain component)” as used herein means that the certain component is not intentionally contained in raw materials and the like, and includes, for example, a case in which a tiny amount (e.g., 0.1 mol % or less) of impurities are inevitably contained.
Hereinafter, each component of the glass composition will be described in greater detail. In an embodiment of the glass composition, SiO2 constitutes the skeleton of glass, may increase the chemical durability, and may serve to reduce the occurrence of cracks when scratches (indentations) are made on the glass surface. In an embodiment, SiO2 may be contained in an amount of 50 mol % or greater to improve the chemical durability. In an embodiment, for sufficient meltability, SiO2 may be contained in the glass composition in an amount of 80 mol % or less.
Al2O3 serves to improve the breakage resistance of glass. That is, Al2O3 may serve to generate a smaller number of fragments when the glass is broken. In addition, Al2O3 may serve as an active component that improves the ion exchange performance during chemical strengthening and increases surface compressive stress after strengthening. In an embodiment, the content of Al2O3 is 1 mol % or greater, such that the above-described function may be effectively performed. In an embodiment, the content of Al2O3 may be 30 mol % or less to maintain the acid resistance and meltability of glass.
B2O3 enhances the chipping resistance of glass and improves the meltability of glass. In an embodiment, B2O3 may be omitted (or contained in the amount of 0 mol %). Alternatively, B2O3 may be contained in an amount of 0.5 mol % or greater to improve the meltability of glass. In such an embodiment, B2O3 may be contained in an amount of 5 mol % or less to suppress the occurrence of striae during melting.
P2O5 improves the ion exchange performance and chipping resistance. In an embodiment, P2O5 may be omitted (0 mol %). Alternatively, P2O5 may be contained in an amount of 0.5 mol % or greater to effectively perform the above-described function. In such an embodiment, P2O5 may be contained in an amount of 4 mol % or less to prevent a significant decrease in breakage resistance and acid resistance.
Li2O serves to form surface compressive stress by ion exchange. Li ions near the glass surface may be exchanged with Na ions or the like through an ion exchange process. Li2O may also serve to improve the breakage resistance of glass. The content of Li2O for effective ion exchange is 3 mol % or greater, and the content of Li2O may be 20 mol % or less in terms of acid resistance.
Na2O serves to form surface compressive stress by ion exchange and improve the meltability of glass. Na ions near the glass surface may be exchanged with K ions or the like through an ion exchange process. In an embodiment, Na2O may be omitted. Alternatively, Na2O may be contained in an amount of 1 mol % or greater to effectively perform the above-described role. If only a Li and Na ion exchange process is performed and a K ion exchange process is not performed, the content of Na2O may be 8 mol % or less for smooth Li and Na ion exchange. If a K ion exchange process is also performed, a larger amount of Na2O may be used. However, also in this case, the content of Na2O may be 20 mol % or less for effective acid resistance.
K2O improves the ion exchange performance and is associated with the breakage resistance. In an embodiment, K2O may be omitted. Alternatively, K2O may be contained in an amount of 0.5 mol % or greater to improve the ion exchange performance. In such an embodiment, the content of K2O may be 10 mol % or less to prevent an excessive decrease in breakage resistance.
MgO serves. In an embodiment, the content of MgO is 3 mol % or greater to effectively increase the surface compressive stress and improve the breakage resistance of chemically strengthened glass. In such an embodiment, the content of MgO may be 20 mol % or less to reduce the occurrence of devitrification during glass melting.
CaO serves to improve the meltability and breakage resistance of glass. In an embodiment, CaO may be omitted. Alternatively, CaO may be contained in a content of 0.5 mol % or greater to effectively improve the meltability and breakage resistance of glass. If the content of CaO is excessively high, the ion exchange performance may be degraded. Accordingly, in such an embodiment, the content of CaO may be 20 mol % or less.
SrO serves to improve the meltability and breakage resistance of glass, similarly to CaO. In an embodiment, SrO may be omitted. Alternatively, SrO may be contained in a content of 0.5 mol % or greater to effectively improve the meltability and breakage resistance of glass. If the content of SrO is excessively high, the ion exchange performance may be degraded. Accordingly, in such an embodiment, the content of SrO may be 20 mol % or less.
BaO serves to improve the meltability and breakage resistance of glass. In an embodiment, BaO may be omitted. Alternatively, BaO may be contained in a content of 0.5 mol % or greater to effectively improve the meltability and breakage resistance of glass. In such an embodiment, BaO may be contained in an amount of 15 mol % or less to prevent an excessive decrease in ion exchange performance.
ZnO serves to improve the meltability of glass. In an embodiment, ZnO may be omitted. Alternatively, ZnO may be contained in a content of 0.25 mol % or greater to significantly exhibit the effect of improving meltability. In such an embodiment, the content of ZnO may be 10 mol % or less to prevent a decrease in weatherability.
TiO2 improves the breakage resistance of chemically strengthened glass. In an embodiment, TiO2 may be omitted. Alternatively, TiO2 may be contained in a content of 0.1 mol % or greater to significantly exhibit the effect of improving breakage resistance when. In such an embodiment, the content of TiO2 may be 1 mol % or less to prevent devitrification during melting.
ZrO2 may increase the surface compressive stress due to ion exchange and improve the breakage resistance of glass. In an embodiment, ZrO2 may be omitted. Alternatively, ZrO2 may be contained in a content of 0.5 mol % or greater to effectively increase the surface compressive stress due to ion exchange and to effectively improve the breakage resistance of glass. In such an embodiment, ZrO2 may be contained in an amount of 8 mol % or less to suppress devitrification during melting.
The glass composition may further include components such as Y2O3, La2O3, Nb2O5, Ta2O5 and Gd2O3 in addition to the components described above. The composition of the glass article 100 may be changed through a molding process, an ion exchange process, and the like, which will be described later.
The composition and composition ratio of the glass composition may be determined in consideration of the strain point of the finished strengthened glass. In general, the viscosity of the glass varies with temperature, and the temperature at which the glass has a viscosity of about 1014.5 poise is defined as a strain point. As the strain point increases, the scratch resistance of glass improves. However, if the strain point excessively increases, the elasticity of the glass article 100 decreases, which may be undesired in terms of product conformity. According to the experimental findings, when the strain point of the glass article 100 is in the range of 530° C. to 540° C., it may have sufficient scratch resistance and appropriate elasticity to ensure product conformity. The strain point may be adjusted by the components and composition ratio of the glass article 100. In an embodiment, the components and composition ratio of the glass composition may be adjusted in the molding step S11 to satisfy the strain point of the above-mentioned range.
The glass composition described above may be molded into a plate glass shape by at least one of various methods known in the art. In one exemplary embodiment, for example, the glass composition may be molded by a float process, a fusion draw process, a slot draw process, or the like.
The glass molded into a flat plate shape may be cut through the cutting step S12. The glass molded into a flat plate shape may have a different size than that of the final glass article 100. In one exemplary embodiment, for example, glass molding may be performed to form a large-area substrate as a mother substrate glass 10a including a plurality of glass articles 100, as shown in
Cutting of the glass 10a may be performed using a cutting knife 20, a cutting wheel, a laser, or the like.
In an exemplary embodiment, the cutting step S12 of glass may be performed before the strengthening step S15 of glass. The glass 10a of a mother substrate may be strengthened at once and then cut into the size of the final glass article 100. However, in this case, the cut surface (e.g., side surface of glass) may be in a non-strengthened state. Accordingly, it may be desired to perform the strengthening step S15 after cutting is completed.
Between the cutting step S12 and the strengthening step S15 of glass, a polishing step before strengthening may be performed. The polishing step may include the side polishing step S13 and the surface polishing step S14 before strengthening. In an exemplary embodiment, after the side polishing step S13 is performed first, the surface polishing step S14 may be performed before strengthening, but the order of polishing may be modified or reversed.
The side polishing step S13 is a step of polishing the side surface of a cut glass 10. In the side polishing step S13, the side surface of the glass 10 is polished to have a smooth surface. In such an embodiment, each side surface of the glass 10 may have a uniform (e.g., even or smooth) surface through the side polishing step S13. In such an embodiment, the cut glass 10 may include one or more cut surfaces. In some cut glasses 10, two side surfaces of four side surfaces may be cut surfaces. In some other cut glasses 10, three side surfaces of four side surfaces may be cut surfaces. In some other cut glasses 10, all of four side surfaces may be cut surfaces. When the side surface is a cut surface, it may have different surface roughness from that of an uncut surface. In addition, even the cut surfaces may have different surface roughness from each other. Therefore, in such an embodiment, each side surface may have uniform surface roughness and the like by polishing each side surface through the side polishing step S13. In such an embodiment, a small crack, which may occur on the side surface, may be removed through the side polishing step S13.
The side polishing step S13 may be performed simultaneously on a plurality of cut glasses 10. In an exemplary embodiment, as shown in
The side polishing step S13 may be performed by a mechanical polishing method or a chemical mechanical polishing method using a polishing apparatus 30. In an exemplary embodiment, two opposite side surfaces of the cut glasses 10 may be polished simultaneously, and then the other two opposite side surfaces may be polished simultaneously, but the disclosure is not limited thereto.
The surface polishing step S14 before strengthening may be performed such that each glass 10 has a uniform surface. The surface polishing step S14 before strengthening may be performed separately for each cut glass 10. However, when a chemical mechanical polishing apparatus 40 is sufficiently large compared to the glass 10, the plurality of glasses 10 may be horizontally arranged and then surface polishing may be performed simultaneously.
The surface polishing step S14 before strengthening may be performed by chemical mechanical polishing. In an exemplary embodiment, the first and second surfaces of the cut glass 10 are polished using the chemical mechanical polishing apparatus 40 and a polishing slurry. The first surface and the second surface may be polished simultaneously. Alternatively, one surface of the first and second surfaces may be polished first and then the other surface of the first and second surfaces may be polished.
After the polishing step S14 before strengthening, the strengthening step S15 is performed. The strengthening step S15 may include chemical strengthening and/or thermal strengthening. In an exemplary embodiment where the glass 10 has a thin thickness of 2 mm or less, e.g., about 0.75 mm or less, a chemical strengthening method may be applied for precise stress profile control. Hereinafter, for convenience of description, exemplary embodiments where a chemical strengthening method is applied to the strengthening step S15 of the glass 10 will be describe in detail, but not being limited thereto.
Chemical strengthening may be performed through an ion exchange process. The ion exchange process is a process of exchanging ions in the glass 10 with other ions. By performing the ion exchange process, the ions at or near the surface of the glass 10 may be replaced or exchanged with larger ions having the same valence or oxidation state. In one exemplary embodiment, for example, where the glass 10 contains a monovalent alkali metal such as Li+, Na+, K+ and Rb+, the monovalent cation on the surface may be replaced by Na+, K+, Rb+, or Cs+ ions with a larger ionic radius. The ion exchange process will hereinafter be described in greater detail with reference to
Referring to
Referring back to
After the strengthening step S15, selectively, the surface polishing step S16 after the strengthening may be further performed. The surface polishing step S16 after strengthening may remove fine cracks on the surface of the strengthened glass 10 and control compressive stress of the first surface and the second surface of the strengthened glass 10. In one exemplary embodiment, for example, a floating method, which is one of methods for producing a glass plate, is performed by flowing a glass composition into a tin bath. In such an embodiment, the surface of the glass plate in contact with the tin bath may have different compositions from the surface not in contact with the tin bath. As a result, after the strengthening step S15 of the glass 10, a deviation in compressive stress may occur between the surface in contact with the tin bath and the surface not in contact with the tin bath. In such an embodiment, the deviation in compressive stress between the contact surface and the non-contact surface may be reduced by removing the surface of the glass 10 to an appropriate thickness by polishing.
The surface polishing step S16 after strengthening may be performed by a chemical mechanical polishing method. In an exemplary embodiment, the first and second surfaces of the strengthened glass 10, which is the glass 10 to be processed, are polished using a chemical mechanical polishing apparatus 60 and a polishing slurry. In an exemplary embodiment, the polishing thickness may be, for example, in a range of about 100 nm to about 1000 nm, but not being limited thereto. The polishing thicknesses of the first surface and the second surface may be the same as each other, or alternatively, may be different from each other.
Although not shown in the drawings, after the surface polishing step S16 after strengthening, a shape machining process may be further performed as desired. In an exemplary embodiment where the glass article having a three-dimensional shape 101, 102 or 103 is produced as shown in
In such an embodiment, as described above, the finished glass article 100 has a strain point in the temperature range of about 530° C. to about 540° C., and thus may have high scratch resistance.
Hereinafter, the stress profile of the strengthened glass article 100 will be described in detail.
Referring to
The first compressive region CSR1 and the second compressive region CSR2 are resistant to an external impact to prevent the occurrence of cracks or breakage of the glass article 100. As the maximum compressive stresses CS1 and CS2 of the first compressive region CSR1 and the second compressive region CSR2 become larger, the strength of the glass article 100 generally increases. Since an external impact is usually transmitted through the surface of the glass article 100, it is desired to have the maximum compressive stresses CS1 and CS2 at the surface of the glass article 100 in terms of durability. Accordingly, in an exemplary embodiment, the compressive stress of the first compressive region CSR1 and the second compressive region CSR2 may be the largest at the surface and generally decrease toward the inside.
The first compression depth DOL1 and the second compression depth DOL2 suppress cracks or grooves formed in the first surface US and the second surface RS from propagating to the tensile region CTR inside the glass article 100. As the first compression depth DOL1 and the second compression depth DOL2 are larger, it is possible to more efficiently prevent propagation of cracks and the like. The point corresponding to the first compression depth DOC1 and the second compression depth DOC2 corresponds to a boundary between the compressive regions CSR1 and CSR2 and the tension region CTR, and has a stress value of zero.
Throughout the glass article 100, the tensile stress of the tensile region CTR may be balanced with the compressive stress of the compressive regions CSR1 and CSR2. That is, the total compressive stress (i.e., the compressive energy) in the glass article 100 may be the same as the total tensile stress (i.e., the tensile energy) in the glass article 100. The stress energy accumulated in one region having a constant width in the thickness t direction in the glass article 100 may be calculated as an integrated value of the stress profile. The following relational expression may be obtained in a case where the stress profile in the glass article 100 having a thickness t is represented as a function f(x).
The greater the magnitude of the tensile stress in the glass article 100, the more likely the fragments are to be vigorously released when the glass article 100 is broken, and the more likely the glass article 100 is to be broken from the inside. The maximum tensile stress that meets a frangibility standard of the glass article 100 may satisfy, but not limited to, the following relationship:
CT1≤−38.7×ln(t)+48.2 [Mathematical Expression 2]
In one exemplary embodiment, the maximum tensile stress CT1 may be about 80 megapascal (MPa) or less, e.g., about 45 MPa or less. The maximum tensile stress CT1 of about 60 MPa or greater may be desirable to improve mechanical properties such as strength. In an exemplary embodiment, the maximum tensile stress CT1 may be greater than or equal to about 65 MPa and less than or equal to about 75 MPa, but not being limited thereto.
The maximum tensile stress CT1 of the glass article 100 may be generally located at a central portion in the thickness t direction of the glass article 100. For example, the maximum tensile stress CT1 of the glass article 100 may be located at a depth in a range of about 0.4 t to about 0.6 t, or in a range of about 0.45 t to about 0.55 t, or at a depth of about 0.5 t. Here, t denotes the thickness of the glass article 100.
In an exemplary embodiment, the compressive stress and the compression depths DOC1 and DOC2 may have large values to increase the strength of the glass article 100. However, as the compressive energy increases, the tensile energy also increases, and the maximum tensile stress CT1 may increase. Accordingly, in such an embodiment, it is desirable to adjust the stress profile in a way such that the maximum compressive stresses CS1 and CS2 and the compression depths DOL1 and DOL2 have large values while the compressive energy becomes smaller to meet the fragility requirements while having high strength. Accordingly, in an exemplary embodiment, each of the first compressive region CSR1 and the second compressive region CSR2 may include a first transition point TP1 and a second transition point TP2 at which the slope of the stress profile changes abruptly. The shape of the stress profile (particularly, the shape of the stress profile in the compressive region) may be precisely controlled by adjusting the process conditions of the primary ion exchange process and the secondary ion exchange process.
Hereinafter, the stress profile of the compressive region will be described in detail with reference to
Referring to
The first transition point TP1 is located between the first surface US and the first compression depth DOC1. The stress profile may be divided into a first segment SG1 and a second segment SG2 based on the first transition point TP1. That is, the stress profile may include the first segment SG1 extending from the first surface US to the first transition point TP1 and the second segment SG2 extending from the first transition point TP1 to the first compression depth DOC1.
As shown in
The stress of the first segment SG1 located relatively near to the first surface US in the first compressive region CSR1 may be mainly determined by the density of potassium ions. In such an embodiment, as described above, the section of the first segment SG1 may further include sodium ions, but the stress of the corresponding section may be mainly dependent on the density of potassium ions having a larger ion size. In the depth section of the first segment SG1, the greater the density of potassium ions is, the higher the stress become, and the stress profile may substantially approximate to the density profile of potassium ions. The first transition point TP1 may correspond to the maximum penetration depth of potassium ions.
The stress of the second segment SG2 located inward relative to the first compressive region CSR1 may be mainly determined by the density of sodium ions. That is, in the depth section of the second segment SG2, the greater the density of sodium ions is, the higher the stress become, and the stress profile may substantially approximate to the density profile of sodium ions. The first compression depth DOC1 may substantially correspond to the maximum penetration depth of sodium ions.
The first segment SG1 may substantially approximate to a first straight line l1 connecting the coordinates of the first transition point TP1 and the coordinates of the first surface US in the corresponding section. The first straight line l1 may be expressed as a first function in Mathematical Expression 3 below in a coordinate plane with an X-axis indicating depth and a Y-axis indicating stress:
y=m1x+a [Mathematical Expression 3]
In Mathematical Expression 3, m1 denotes a first slope of the first straight line l1, and a is a y-intercept, which represents the compressive stress at the first surface US.
The second segment SG2 may substantially approximate to a second straight line l2 connecting the coordinates of the first transition point TP1 and the coordinates of the first compression depth DOC1 having a stress value of zero in the corresponding section. The second straight line l2 may be expressed as a second function in Mathematical Expression 4 below in a coordinate plane with an X-axis indicating depth and a Y-axis indicating stress:
y=m2x+b [Mathematical Expression 4]
In Mathematical Expression 4, m2 denotes an average slope of the second segment SG2, which is a second slope of the second straight line l2, b denotes a y-intercept, and −b/m2 is an x-intercept, which represents the first compression depth DOC1.
Some sections of the tensile region CTR adjacent to the first compressive region CSR1 may have a stress profile in conformity with the second straight line l2.
In the above functions, each of the first slope m1 and the second slope m2 has a negative value, and the absolute value of the first slope m1 of the first straight line l1 is greater than the absolute value of the second slope m2 of the second straight line l2. The first segment SG1 may substantially have the first slope m1, and the second segment SG2 may substantially have the second slope m2.
The slope (or gradient) of the stress profile changes abruptly at the first transition point TP1. The first transition point TP1 is located at a point where the first straight line l1 and the second straight line l2 meet each other, but the second segment SG2 and the first segment SG1 in the actual stress profile have an inflection point around the first transition point TP1 at which the actual stress profile is curved. The stress profile may have a third slope m3 at the first transition point TP1, and the third slope m3 may be calculated as a slope of a tangent line l3 of the stress profile at the first transition point TP1. The third slope m3 may approximate to a slope of a straight line connecting one point of the first segment SG1 adjacent to the first transition point TP1 and one point of the second segment SG2. The tangent line l3 at the first transition point TP1 may be expressed as a third function in Mathematical Expression 5 below:
y=m3x+C [Mathematical Expression 5]
The third slope m3 has a negative value, and the absolute value of the third slope m3 may be less than the absolute value of the first slope m1 and greater than the absolute value of the second slope m2.
In an exemplary embodiment, the absolute value of the third slope m3 of the third function may be in a range of about 9 MPa/μm to about 12 MPa/μm. In an alternative exemplary embodiment, the absolute value of the third slope m3 of the third function may be in a range of about 10 MPa/μm to about 11 MPa/μm. In an exemplary embodiment, the y-intercept of the third function may be in a range of about 270 MPa to about 300 MPa. In one exemplary embodiment, for example, m3 may be about −10.249 MPa/μm and c may be about 292.5 MPa. When the third slope m3 and y-intercept of the third function are in the above-mentioned ranges, respectively, the magnitude of compressive energy and a stress-depth ratio CDR of the first transition point TP1 may be within desired ranges to be described later.
In an exemplary embodiment, the first segment SG1 and the second segment SG2 having different slopes from each other may be generated by a plurality of ion exchange processes. The second segment SG2 may be generated through the primary ion exchange process, and the first segment SG1 may be generated through the secondary ion exchange process.
In such an embodiment, the primary ion exchange process is a process of imparting the compression depths DOC1 and DOC2 to the glass, and may be performed generally by exposing the glass to single molten salt containing sodium ions or mixed molten salt containing potassium ions and sodium ions. In one exemplary embodiment, for example, for the primary ion exchange process, the glass is immersed in a first bath 51 (see
The primary ion exchange process may be performed at a temperature in a range of ±20° C. from a temperature 50° C. lower than the glass transition temperature. In one exemplary embodiment, for example, where the glass transition temperature is about 580° C., the primary ion exchange process may be performed at a temperature of about 500° C. or higher. The primary ion exchange process time may be in a range from 3 hours to 8 hours, but not being limited thereto.
Through the primary ion exchange process, lithium ions/sodium ions which are small ions inside the glass are exchanged with sodium ions/potassium ions which are larger ions than lithium ions/sodium ions in the molten salt, thereby increasing the concentration of sodium ions and/or potassium ions in the glass. Since the molten salt is provided with lithium ions from the glass, the molten salt of the first bath after the primary ion exchange process may further include lithium ions in addition to sodium ions and potassium ions.
After the primary ion exchange process and before the secondary ion exchange process, a stress relieving process (or an annealing process) may be further performed. The stress relieving process may be performed at a temperature of about 500° C. or higher for 1 hour to 3 hours. The stress relieving process may reduce the maximum compressive stress and allow the diffusion of sodium ions (and/or potassium ions) into the glass to increase the compressive depth. The stress relieving process may be performed in air or liquid. Alternatively, the stress relieving process may be omitted.
Upon completion of the primary ion exchange process (if a stress relieving process is additionally performed, when the stress relieving process is completed), a stress profile corresponding to the second straight line l2 is generated in the glass article 100. That is, sodium ions and/or potassium ions of the mixed molten salt are exchanged to penetrate into the glass, and then diffuse in the depth direction. Sodium ions generally diffuse to the first compression depth DOC1 to form the first compressive region CSR1 having a compressive stress from the first surface US to the first compressive depth DOC1. That is, the first compression depth DOC1 is determined by the primary ion exchange process and/or the stress relieving process.
The density of diffusing ions is substantially inversely proportional to the diffusion distance. Since sodium ions and potassium ions enter the glass through ion exchange from the surface of the glass and diffuse in the depth direction, the concentration of sodium ions and potassium ions tends to substantially linearly decrease as it goes away from the first surface US of the glass. As a result, the stress profile has the largest stress CS1_1 at the first surface US1 of the glass and decreases in the depth direction in the same manner as the second straight line l2.
In addition, the degree of diffusion of ions is inversely proportional to the size of ions. In other words, as the size of ions is smaller, more ions diffuse. Therefore, when both sodium ions and potassium ions penetrate into the glass through the first ion exchange process, sodium ions having a relatively small size may diffuse more readily and penetrate deeper into the glass article 100. Sodium ions may diffuse to the first compression depth DOC1, while potassium ions may diffuse only to a depth less than or equal to the first transition point TP1.
In such an embodiment, as described above, the first compression depth DOC1 has a close correlation with the maximum diffusion depth of sodium ions, which are smaller ions that are ion-exchanged. The first compression depth DOC1 may be the same as the maximum diffusion depth of sodium ions, or may be located in the vicinity thereof even though there is a slight difference, and may be generally proportional to the maximum diffusion depth of sodium ions. As described above, the primary ion exchange process and/or the stress relieving process is a process of forming a predetermined first compression depth DOC1 through sufficient diffusion, and is performed for a sufficiently long time to allow ions to be sufficiently diffused.
In such an embodiment, as more ion diffusion is performed, the maximum compressive stress CS1 may become smaller. The maximum compressive stress CS1 increases as the density of ions increases. Thus, if a same amount of ions enter into the glass, the more the diffusion become, the smaller the density of ions and the smaller the compressive stress become. As described above, since the primary ion exchange process has limitations to increasing the maximum compressive stress CS1 of the first surface US, the secondary ion exchange process is further performed after the primary ion exchange process to form a greater surface compressive stress CS1.
The secondary ion exchange process is a process of increasing the maximum compressive stress CS1, and is generally performed by exposing the glass to single molten salt containing potassium ions or mixed molten salt containing potassium ions and sodium ions. In one exemplary embodiment, for example, for the secondary ion exchange process, the glass that has undergone the primary ion exchange process is immersed in the second bath 52 (see
The secondary ion exchange process may be performed at a lower temperature and for a shorter time than the primary ion exchange process. In one exemplary embodiment, for example, the secondary ion exchange process may be performed for 1 hour to 3 hours, or 1.3 hours to 2 hours in a temperature range of about 380° C. to about 460° C.
Through the secondary ion exchange process, the compressive stress in a shallow depth section of the glass surface US is substantially increased. In an exemplary embodiment, where potassium ions penetrate into the glass, the compressive stress in the corresponding portion becomes larger due to the potassium ions having a larger size. Potassium ions which penetrate into the glass diffuse in the depth direction. Compared with the primary ion exchange process, potassium ions have a slower diffusion rate than sodium ions, and the duration of the secondary ion exchange process is shorter than that of the primary ion exchange process. Accordingly, the diffusion depth of potassium ions diffused through the secondary ion exchange process may be much less than that in the first compression depth DOC1. The maximum diffusion depth of potassium ions may be equal to or less than the first transition point TP1, as described above.
The stress profile formed by the potassium ions additionally penetrated through the secondary ion exchange process has substantially the same shape as in the first straight line l1. The compressive stress CS1 of the first surface US is increased through the secondary ion exchange process, while the penetration depth (or the first transition point TP1) of the potassium ions is less than the first compressive depth DOC1. Thus, the absolute value of the first slope m1 of the first straight line l1 is greater than the absolute value of the second slope m2 of the second straight line l2. That is, the compressive stress profile may have a slope which is steep in the vicinity of the surface of the glass article 100, and becomes gentler toward the interior of the glass article 100.
The stress profile in the first compressive region CSR1 as described above may have at least three main feature points.
A first feature point corresponds to the y-intercept of the second straight line l2 and is located on the first surface US. A second feature point corresponds to the x-intercept of the first straight line l1, and corresponds to the first compression depth DOC1. A third feature point is located at the first transition point TP1. The position of the feature point is a factor that substantially determines the stress profile. Since the stress profile between the first feature point and the third feature point approximates to the first straight line l1, and the stress profile between the second feature point and the third feature point approximates to the second straight line l2, when the first feature point, the second feature point and the third feature point are determined, the shape of the stress profile may also be determined.
The first feature point is a point located on the first surface US, and has an x-coordinate value of 0 and a y-coordinate value which corresponds to the maximum compressive stress CS1. The maximum compressive stress CS1 expressed by the first feature point is associated with the strength of the glass article 100. In an exemplary embodiment, the occurrence of cracks due to external impacts may be effectively prevented by increasing the maximum compressive stress CS1. The maximum compressive stress CS1 is mainly determined by the amount of potassium ions exchanged in the secondary ion exchange process, and may have a certain relationship with the degree of diffusion after ion exchange.
In an exemplary embodiment, the maximum compressive stress CS1 may be about 300 MPa or greater. In exemplary embodiments, for example, the maximum compressive stress CS1 may be about 350 MPa or greater, about 400 MPa or greater, about 450 MPa or greater, or about 500 MPa or greater. In addition, the maximum compressive stress CS1 may be about 2000 MPa or less. In such embodiments, the maximum compressive stress CS1 may be about 1800 MPa or less, about 1500 MPa or less, or about 1050 MPa or less. In one exemplary embodiment, for example, the maximum compressive stress CS1 may be in a range of about 780 MPa to about 820 MPa.
The second feature point is a point where the stress value is 0, and has a y-coordinate value of 0 and an x-coordinate value which corresponds to the first compression depth DOC1. The first compression depth DOC1 represented by the second feature point corresponds to the size (or width) of the first compressive region CSR1 of the glass article 100. In an exemplary embodiment, cracks may be effectively prevented from propagating to the tensile region CTR by increasing the first compression depth DOC1. Accordingly, in an exemplary embodiment, the first compression depth DOC1 (i.e., the distance from the first surface US to the first compression depth DOC1) may be about 50 micrometers (μm) or greater, about 65 μm or greater, about 80 μm or greater, or about 95 μm or greater. However, if the first compression depth DOC1 is excessively large, the compressive energy and the tensile energy may become excessively great, which may cause failure in satisfying a frangibility standard. Accordingly, in an exemplary embodiment, the first compression depth DOC1 may be about 250 μm or less, about 200 μm or less, about 180 μm or less, about 150 μm or less, or about 135 μm or less. In one exemplary embodiment, for example, the first compression depth DOC1 may be in a range of about 110 μm to about 120 μm.
The first compression depth DOC1 may be controlled mainly by the temperature and time duration of the primary ion exchange process and/or the stress relieving process.
In an exemplary embodiment, the first compression depth DOC1 may be about 0.1 t or greater, about 0.15 t or greater, or about 0.18 t or greater, where the thickness of the glass is t. In such an embodiment, the first compression depth DOC1 may be about 0.25 t or less, about 0.23 t or less, or about 0.2 t or less, where the thickness of the glass is t.
The third feature point is located at a predetermined depth and has a predetermined stress value. The first transition point TP1 represented by the third feature point is mainly associated with the first slope m1 of the first segment SG1 and the second slope m2 of the second segment SG2. The first slope m1 may be determined by process conditions of the primary ion exchange process and the stress relieving process, and the second slope m2 may be determined by process conditions of the secondary ion exchange process.
The x-coordinate value (depth) of the first transition point TP1 has a value between 0 and the first compression depth DOC1, and the y-coordinate value (stress) of the first transition point TP1 has a value between 0 and the maximum compressive stress. According to the example of the first compression depth DOC1 and the maximum compressive stress CS1 as described above, the depth of the first transition point TP1 may be in a range of about 0 μm to about 9.0 μm, and the stress of the first transition point TP1 may be in a range of about 0 MPa to about 220 MPa. The position of the first transition point TP1 determines the substantial shape of the stress profile in the first compressive region CSR1. In addition, the position of the first transition point TP1 determines the area of the first compressive region CSR1, i.e., the magnitude of the compression energy.
If a depth DOL_TP1 of the first transition point TP1 is excessively large, the production cost may increase, the magnitude of compressive energy may be excessively large, or mechanical properties such as strength may be degraded. If the depth DOL_TP1 of the first transition point TP1 is excessively small, a section capable of efficiently preventing the propagation of cracks due to a strong impact may be reduced. In view of the above, the depth DOL_TP1 of the first transition point TP1 may be in the range of about 8.1 μm to about 9.5 μm.
The ratio of the depth DOL_TP1 of the first transition point TP1 to the first compression depth DOC1 may be in a range of about 0.065 to about 0.095, or in a range of about 0.07 to about 0.08. The depth DOL_TP1 of the first transition point TP1 may be in the range of about 0.010 t to about 0.015 t or in the range of about 0.011 t to about 0.014 t with respect to the thickness t of the glass.
The stress CS_TP1 of the first transition point TP1 may be about 150 MPa or greater, about 180 MPa or greater, or about 197 MPa or greater. In addition, the stress CS_TP1 of the first transition point TP1 may be about 250 MPa or less, about 230 MPa or less, or about 207 MPa or less. If the stress CS_TP1 of the first transition point TP1 is excessively great, the compressive energy increases or the depth of the first transition point TP1 becomes small, such that the propagation of cracks may not be effectively prevented. If the stress CS_TP1 of the first transition point TP1 is excessively little, the strength may become excessively small. Accordingly, in an exemplary embodiment, the stress CS_TP1 of the first transition point TP1 may be in a range of about 150 MPa to about 250 MPa. In such an embodiment, the stress CS_TP1 of the first transition point TP1 may be in a range of about 180 MPa to about 230 MPa. In such an embodiment, the stress CS_TP1 of the first transition point TP1 may be in a range of about 197 MPa to about 207 MPa. The stress CS_TP1 of the first transition point TP1 may be in a range of about 0.220 times to about 0.260 times the maximum compressive stress CS1, or in a range of about 0.230 times to about 0.255 times the maximum compressive stress CS1.
In addition to the depth DOL_TP1 and the stress CS_TP1 of the first transition point TP1, the ratio of the stress CS_TP1 to the depth DOL_TP1 (hereinafter, referred to as a stress-depth ratio CDR) of the first transition point TP1 is a major factor in determining a proportion of the compressive energy (i.e., a value obtained by integrating each segment) of each segment SG1, SG2 in the stress profile.
As shown in
The crack prevention stress CS_50 of the crack prevention point P50 may have a value greater than zero and less than the stress CS_TP1 of the first transition point TP1, but not being limited thereto. In an exemplary embodiment, the crack prevention stress CS_50 may have a value of about 55 MPa or greater, about 65 MPa or greater, or about 75 MPa or greater. In such an embodiment, the crack prevention stress CS_50 may be about 100 MPa or less, about 90 MPa or less, or about 80 MPa or less. In one exemplary embodiment, for example, the crack prevention stress CS_50 may have a value in a range of about 55 MPa to about 100 MPa. In such an embodiment, the crack prevention stress CS_50 may have a value in a range of about 65 MPa to about 90 MPa. In such an embodiment, the crack prevention stress CS_50 may have a value in a range of 75 MPa to 80 MPa, but not being limited thereto.
The stress profile shown in
In addition, the stress profile illustrated in
Referring to
According to the experimental findings shown in
Referring to
With respect to the second compressive energy, the range of the second compressive energy capable of improving the mechanical property and satisfying the frangibility standard may be in a range of about 5,500 J/m2 to about 8,500 J/m2. In an exemplary embodiment, the second compressive energy may be in a range of about 7,000 J/m2 to about 8,000 J/m2. In one exemplary embodiment, for example, the second compressive energy may be in a range of about 7,250 J/m2 to about 7,750 J/m2.
Further, with respect to the first compressive energy, the range of the first compressive energy capable of improving the mechanical property and satisfying the frangibility standard may be in a range of about 3,200 J/m2 to about 4,000 J/m2. In an exemplary embodiment, the first compressive energy may be in a range of about 3,400 J/m2 to about 3,800 J/m2. In one exemplary embodiment, for example, the first compressive energy may be in a range of about 3,500 J/m2 to about 3,700 J/m2.
In an exemplary embodiment, the compressive energy of the first compressive region CSR1, i.e., the sum of the first compressive energy and the second compressive energy may be in a range of about 8,700 J/m2 to about 12,500 J/m2. In one exemplary embodiment, for example, the compression energy of the first compressive region CSR1 may be in a range of about 10,500 J/m2 to about 11,500 J/m2.
The tensile energy is the sum of the compressive energy of the first compressive region CSR1 and the compressive energy of the second compressive region CSR2, and is equal to twice the compressive energy of each compressive region. Thus, in consideration of the mechanical property and frangibility standard, the tensile energy may range from 16,000 J/m2 to 24,000 J/m2.
The compressive stress, the first compressive depth DOC1, the tensile stress, the first transition point TP1 and the like described herein may be measured by a surface stress meter and/or a scattered light photoelastic stress meter.
Specifically, the first segment SG1 associated with the surface compressive stress CS1 and the first transition point TP1 may be measured by a surface stress meter such as FSM-6000 manufactured by Orihara Industrial Co., Ltd. (Japan). The surface stress meter may measure the density of potassium ions in the glass article 100. Therefore, the first segment SG1 of the stress profile may be estimated by measuring the density of potassium ions from the first surface US of the glass article 100 to the first transition point TP1, which is the maximum penetration depth of potassium ions.
The tensile stress may be measured by a scattered light photoelastic stress meter such as SLP-1000 manufactured by Orihara Industrial Co., Ltd. The scattered light photoelastic stress meter can measure the stress inside the glass article 100 using a laser and scattered light photoelastic analysis technology, and is mainly used to measure the tensile stress of the tensile region CTR. The tensile stress is the largest at the center of the glass article 100 and has a stress value of zero when it reaches the first compression depth DOC1. Therefore, a point where the stress value measured by the scattered light photoelastic stress meter is zero may be estimated as the first compression depth DOC1, and the second segment SG2 may be estimated by connection from the first compression depth DOC1 to the first transition point TP1.
However, the method of measuring the stress profile is not limited to the above-mentioned method, but the stress profile may be measured by using at least one of various other apparatuses and methods known in the art.
Hereinafter, exemplary embodiments will be described in greater detail with reference to
Referring to
A plurality of plate-shaped glass substrates having a thickness of about 0.70 millimeter (mm) and having a lithium aluminosilicate composition were prepared, and a chemical strengthening process was performed to produce Sample Groups A, B and C which have similar stress profiles, but have different strain points.
As the chemical strengthening process, a primary ion exchange process was performed on the glass substrates by immersing the glass substrates in a first molten salt bath in which potassium nitrate and sodium nitrate are mixed in a salt ratio of about 50:50, and a secondary ion exchange process was performed by immersing the glass substrates in a second molten salt bath in which potassium nitrate and sodium nitrate are mixed in a salt ratio of about 98:2. For comparison of strengths according to stress profiles, the ion exchange process was performed on each sample group in a different bath such that each sample group has a different stress profile, controlling temperature and time of the ion exchange process. The process conditions were adjusted such that the maximum compressive stress of each sample group corresponds to about 810 MPa±40 MPa.
With respect to the glass substrates on which the strengthening process has been completed, the stress at each position in the thickness direction, compression depth and energy were measured by FSM-6000 and SLP-1000, and the results are shown in Table 1 below and shown in
In addition, a tangent line equation at the transition point of each sample group was calculated as follows.
The strain point of the glass was measured using thermomechanical analysis (“TMA”) of measuring a change in size of the sample as a function of temperature by applying a load while varying the temperature of the sample and differential thermal analysis (“DTA”) of measuring a temperature difference between the sample and a reference material as a function of temperature while varying the temperature of the sample and the reference material.
Sample Group A exhibited values of 525° C. to 535° C. (e.g., about 530° C.) at strain points measured with 100 samples. Sample Group B exhibited values of 530° C. to 540° C. (e.g., about 535° C.) at strain points measured with 100 samples. Sample Group C exhibited values of 496° C. to 506° C. (e.g., about 501° C.) at strain points measured with 100 samples.
The hardness H of the glass may be obtained through the following equation by applying a load P to the sample with a triangular pyramid-shaped Berkovich tip using a nano indenter and measuring a triangular indentation area A. In an exemplary embodiment, the load P may be about 1 newton (N) and the distance from the center of the Berkovich tip to the vertex may be about 20 nanometers (nm).
In the hardness measurement evaluation, an average value of hardness of 7.904 GPa was measured in Sample Group A, an average value of hardness of 8.082 GPa was measured in Sample Group B, and an average value of hardness of 8.159 GPa was measured in Sample Group C. The tendency of hardness was substantially consistent with the tendency of maximum compressive stress. Sample Group C with the highest maximum compressive stress exhibited the highest hardness, and Sample Group A with the lowest maximum compressive stress exhibited the lowest hardness.
Critical scratch load evaluation was performed. A critical scratch load is a measure to evaluate the scratch resistance. The critical scratch load refers to a load at which a scratch begins to occur when increasing a load from about 0 N to about 15 N on an about 2 mm long region of the sample with a pyramidal diamond tip having a diagonal length of about 19 μm by using a Vickers hardness tester. Table 3 shows the average value of the critical scratch load for each sample group.
Referring to Table 3, in the critical scratch load evaluation, an average value of critical scratch load of 9.3 N was measured in Sample Group A, an average value of critical scratch load of 9.9 N was measured in Sample Group B, and an average value of critical scratch load of 6.1 N was measured in Sample Group C. The tendency of critical scratch load was not substantially consistent with the tendency of maximum compressive stress. On the other hand, the tendency of critical scratch load was substantially consistent with the tendency of strain point. Sample Groups A and B having similar strain points exhibited similar critical scratch load values, and Sample Group C, which has a relatively low strain point compared with Sample Groups A and B, exhibited a low critical scratch load value.
Referring to
Glass impact test (“GIT”) evaluation was performed. For the evaluation according to Experimental Example 2, 100 samples for each of Sample Groups A, B and C were prepared. GIT evaluation was performed by placing and fixing a strengthened glass sample on a ring, and then dropping a 60 g ball onto the surface of the sample to check the height at which the sample is broken. Herein, the 60 g ball is a ball having a weight of about 60 grams (g). If a crack does not occur when dropping the ball, the ball drop was repeated by increasing the height by 5 cm. Finally, when a crack has occurred, the height (i.e., the maximum height at which no crack occurred) immediately before the occurrence of the crack was determined as a critical drop height. Table 4 shows the average value of the critical drop height for each sample group.
With reference to Table 4, in the GIT evaluation, an average value of critical drop height of 33.7 cm was measured in Sample Group A, and an average value of critical drop height of 29.2 cm was measured in Sample Group C. On the other hand, an average value of critical drop height of 49.2 cm was measured in Sample Group B having a smaller maximum compressive stress than Sample Group C. Thus, Sample Group B was evaluated to have a much higher surface strength than Sample Group C. That is, in the GIT evaluation using a 60 g ball for 100 samples, Sample Group B exhibited an average value of critical drop height of about 49 cm or greater, which indicates that Sample Group B has high surface strength.
Critical drop height evaluation was performed. Referring to
After dropping the jig model 600 to which Sample Group A, B, C is applied, if a crack does not occur, the drop of the jig model 600 was repeated by increasing the height by 5 cm. Finally, when a crack has occurred, the height (i.e., the maximum height at which no crack occurred) immediately before the occurrence of the crack was determined as a critical drop height h.
As represented in Mathematical Expression 7 above, the factors affecting the critical drop height h include a horizontal length L1, a vertical length L2 and a height L3 of the jig model 600, Young's modulus Ecomp of the jig model 600 including glass, a weight m of the jig model 600, a compressive stress CS_50 at a depth of 50 μm from the surface of a glass sample, fracture toughness KIC of the glass sample, a constant Y according to the crack shape, a crack length c, an extinction coefficient α which is defined as a ratio of bending energy to total kinetic energy, Young's modulus Eglass of the glass sample, and the like.
The compressive stress affecting the critical drop height h is the compressive stress CS_50 at a depth of 50 μm from the surface. As the experimental result, as described above, since the depth of the crack generated in each sample has a median of about 50 μm, the stress at the depth point of the crack, i.e., the compressive stress CS_50 at the depth point of 50 μm from the glass surface may have a significant effect on the critical drop height h.
As a result of the critical drop height evaluation, the average value of the critical drop height for each sample group is shown in Table 5.
With reference to Table 5, in the model critical drop height evaluation, an average value of critical drop height of 44.7 cm was measured in Sample Group A, and an average value of critical drop height of 39.7 cm was measured in Sample Group C. On the other hand, an average value of critical drop height of 63.2 cm was measured in Sample Group B which has a smaller maximum compressive stress than Sample Group C, but has a high strain point and exhibits high scratch resistance according to the results of Experimental Example 1. Thus, Sample Group B was evaluated to have a much higher surface strength than Sample Group C. That is, in the model critical drop height evaluation for 100 samples, Sample Group B exhibited an average value of critical drop height of 60 cm or greater, which indicates that Sample Group B has high surface strength.
The invention should not be construed as being limited to the exemplary embodiments set forth herein. Rather, these exemplary embodiments are provided so that this disclosure will be thorough and complete and will fully convey the concept of the invention to those skilled in the art.
While the invention has been particularly shown and described with reference to embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit or scope of the invention as defined by the following claims.
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