High damage resistance three-layers laminate glass with low central tension

Abstract

A glass article includes a core glass comprising a first major surface and a second major surface. A first clad layer is fused to the first major surface and a second clad layer is fused to the second major surface. The core glass, the first clad layer, and the second clad layer are formed of a borosilicate glass comprising SiO2 > 74 mol%, B2O3 > 10 mol%, and Al2O3 less than 4 mol%.

Description

HIGH DAMAGE RESISTANCE THREE-LAYERS LAMINATE GLASS WITH LOW CENTRAL TENSIONCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of priority to U.S. Provisional Patent Application No. 63 / 602,862 filed on November 27, 2023, the content of which is incorporated herein by reference in its entirety for all purposes.BACKGROUND

[0002] The disclosure relates to glass compositions and glass articles made therefrom, and more particularly to borosilicate glass compositions capable of being formed with a low central tension and glass articles made therefrom.

[0003] Glass is used in windows due to its optical clarity and durability. Automotive and architectural windows may include a single glass ply or a laminate that includes two glass clad layers with a core disposed in between. The core is typically formed of soda-lime glass that must undergo tempering processes to provide high strength for sharp contact damage. However, even after tempering processes, soda-lime glass is susceptible to thermal shock and crack propagation upon impact. One of the reasons for crack propagation in traditional systems is that traditional laminates include a high amount of built-in compressive stress. Accordingly, there is a need for laminate structures that exhibit lower crack propagation in conjunction with high damage resistance.SUMMARY

[0004] According to one embodiment, a glass article includes a core glass comprising a first major surface and a second major surface. A first clad layer is fused to the first major surface and a second clad layer is fused to the second major surface. The core glass, the first clad layer, and the second clad layer are formed of a borosilicate glass comprising SiO2 > 74 mol%, B2O3 > 10 mol%, and A12O3 less than 4 mol%.

[0005] According to another embodiment, a glass article includes a core glass formed of a borosilicate glass that comprises a first major surface and a second major surface. The coreglass has a first coefficient of thermal expansion (CTE). A first clad layer is fused to the first major surface and a second clad layer is fused to the second major surface. The first clad layer and the second clad layer are formed of a borosilicate glass and have a second CTE that is less than the first CTE. The first and second clad layers have a compressive stress that imparts a tensile stress on the core glass of less than 10 MPa.

[0006] According to yet another embodiment, a glass article includes a core glass comprising a first major surface and a second major surface. The core glass has a first coefficient of thermal expansion (CTE). A first clad layer is fused to the first major surface and a second clad layer is fused to the second major surface. The first clad layer and the second clad layer have a second CTE that is less than the first CTE. The glass article further includes a failure height greater than 500 mm when subjected to a Vickers dart test. The Vickers dart test includes utilizing a Vickers dart that has a weight of 8.5 g. When the Vickers dart test is subjected above the failure height, one or more of the core glass, the first clad layer, and the second clad layer will exhibit a cone crack.

[0007] Additional features and advantages will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the embodiments as described herein, including the detailed description which follows, the claims, as well as the appended drawings.

[0008] It is to be understood that both the foregoing general description and the following detailed description are merely exemplary and are intended to provide an overview or framework to understanding the nature and character of the claims.

[0009] The accompanying drawings are included to provide a further understanding of principles of the disclosure, and are incorporated in, and constitute a part of, this specification. The drawings illustrate one or more embodiment s) and, together with the description, serve to explain, by way of example, principles and operation of the disclosure. It is to be understood that various features of the disclosure disclosed in this specification and in the drawings can be used in any and all combinations. By way of non-limiting examples, the various features of the disclosure may be combined with one another according to the following embodiments.BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The following is a description of the figures in the accompanying drawings. The figures are not necessarily to scale, and certain features and certain views of the figures may be shown exaggerated in scale or in schematic in the interest of clarity and conciseness.

[0011] FIG. 1 is a cross-sectional schematic view of a laminate glass article comprising glass core and clad layers, according to at least one example of the disclosure;

[0012] FIG. 2 is a cross-sectional schematic view plot of a laminate overflow distributor apparatus for making laminate glass articles, according to at least one example of the disclosure;

[0013] FIG. 3A is a graphical representation of a coefficient of thermal expansion (CTE) as a function of temperature for a laminate glass article, according to at least one example of the present disclosure;

[0014] FIG. 3B is a graphical representation of a CTE as a function of temperature for a comparative example of a laminate glass article;

[0015] FIG. 4 is a graphical representation of results from a Vickers dart drop test of a laminate glass article and several comparative examples, according to at least one example of the present disclosure;

[0016] FIG. 5 is a graphical representation of failure values from a Vickers dart drop test of a laminate glass article and several comparative examples, according to at least one example of the present disclosure;

[0017] FIG. 6A is a series of images illustrating results from a Gravelometer test of a comparative example of a laminate glass article;

[0018] FIG. 6B is a series of images illustrating results from a Gravelometer test of a laminate glass article, according to at least one example of the present disclosure;

[0019] FIG. 7A is a series of images illustrating results from a poke test of a comparative example of a laminate glass article;

[0020] FIG. 7B is a series of images illustrating results from a poke test of a laminate glass article, according to at least one example of the present disclosure;

[0021] FIG. 8A is a pair of microscopy images illustrating results from a poke test after a 48 hour period of a comparative example of a laminate glass article; and

[0022] FIG. 8B is a pair of microscopy images illustrating results from a poke test after a 48 hour period of a laminate glass article, according to at least one example of the present disclosure.DETAILED DESCRIPTION

[0023] Additional features and advantages will be set forth in the detailed description which follows and will be apparent to those skilled in the art from the description, or recognized by practicing the embodiments as described in the following description, together with the claims and appended drawings.

[0024] As used herein, the term “and / or,” when used in a list of two or more items, means that any one of the listed items can be employed by itself, or any combination of two or more of the listed items can be employed. For example, if a composition is described as containing components A, B, and / or C, the composition can contain A alone; B alone; C alone; A and B in combination; A and C in combination; B and C in combination; or A, B, and C in combination.

[0025] In this document, relational terms, such as first and second, top and bottom, and the like, are used solely to distinguish one entity or action from another entity or action, without necessarily requiring or implying any actual such relationship or order between such entities or actions.

[0026] Modifications of the disclosure will occur to those skilled in the art and to those who make or use the disclosure. Therefore, it is understood that the embodiments shown in the drawings and described above are merely for illustrative purposes and not intended to limit the scope of the disclosure, which is defined by the following claims, as interpreted according to the principles of patent law, including the doctrine of equivalents.

[0027] For purposes of this disclosure, the term "coupled" (in all of its forms: couple, coupling, coupled, etc.) generally means the joining of two components directly or indirectly to one another. Such joining may be stationary in nature or movable in nature. Such joining may be achieved with the two components and any additional intermediate members being integrally formed as a single unitary body with one another or with the two components. Such joining may be permanent in nature, or may be removable or releasable in nature, unless otherwise stated.

[0028] As used herein, the term “about” means that amounts, sizes, formulations, parameters, and other quantities and characteristics are not and need not be exact, but may be approximate and / or larger or smaller, as desired, reflecting tolerances, conversion factors, rounding off, measurement error and the like, and other factors known to those of skill in the art. When the term “about” is used in describing a value or an end-point of a range, the disclosure should be understood to include the specific value or end-point referred to. Whether or not a numerical value or end-point of a range in the specification recites “about,” the numerical value or end-point of a range is intended to include two embodiments: one modified by “about,” and one not modified by “about.” It will be further understood that the end-points of each of the ranges are significant both in relation to the other end-point, and independently of the other end-point.

[0029] The terms “substantial,” “substantially,” and variations thereof as used herein are intended to note that a described feature is equal or approximately equal to a value or description. For example, a “substantially planar” surface is intended to denote a surface that is planar or approximately planar. Moreover, “substantially” is intended to denote that two values are equal or approximately equal. In some embodiments, “substantially” may denote values within about 10% of each other, such as within about 5% of each other, or within about 2% of each other.

[0030] Directional terms as used herein — for example up, down, right, left, front, back, top, bottom — are made only with reference to the figures as drawn and are not intended to imply absolute orientation.

[0031] As used herein the terms "the," "a," or "an," mean "at least one," and should not be limited to "only one" unless explicitly indicated to the contrary. Thus, for example, reference to "a component" includes embodiments having two or more such components unless the context clearly indicates otherwise.

[0032] As also used herein, the terms “laminate glass article” and “glass article” are used in their broadest sense to include any object made wholly or partly of glass and / or glassceramics. Unless otherwise specified, all compositions are expressed in terms of weight percent (wt.%). Coefficients of thermal expansion (CTE) are expressed in terms of 10"7 / °C and represent a value measured over a temperature range from about 20°C to about 300°C, unless otherwise specified.

[0033] The terms “relatively low CTE” and “low CTE” are used interchangeably in the disclosure with regard to clad glass layers with a starting glass composition (e.g., prior todrawing, laminating, and ion exchange) having a CTE that is lower than the CTE of the starting composition of the core glass by at least about 5 x 10"7 / °C. Conversely, the terms “relatively high CTE” and “high CTE” are used interchangeably in the disclosure with regard to core glass layers with a starting glass composition having a CTE that is higher than the CTE of the starting composition of the clad glass by at least about 5 x 10"7 / °C. The CTE of clad glass layers may also be lower than the CTE of the core glass layer by an amount in the range from about 5 x 10"7 / °C to about 70 x 10"7 / °C, from about 10 x 10"7 / °C to about 70 x 10"7 / °C, from about 10 x 10"7 / °C to about 60 x 10"7 / °C, or from about 10 x 10"7 / °C to about 50 x 10"7 / °C. For example, the core glass may have a CTE of about 100 x 10"7 / °C and the clad glass layers may have a CTE of about 50 x 10"7 / °C, such that there is a difference of about 50 x 10-7 / °C between the CTE of the core glass and the clad glass layers.

[0034] The terms “mechanically strengthened laminate glass article” and “mechanical strengthening” are used in relation to the laminate glass articles of the disclosure to mean a laminate glass article that has been formed by laminating a high CTE core glass to low CTE clad glass layers, thereby creating compressive stresses in the clad glass layers when the laminate is cooled following lamination. These compressive stresses can offset externally applied mechanical stresses, which have the net effect of strengthening the laminate.

[0035] In general, the disclosure is directed to glass articles, including laminate glass articles with residual compressive stress (i.e., through CTE mismatch between the core and clad glass layers) and viscosity characteristics suitable for various curved and planar glass applications, including for automotive and architectural glazing. The disclosure also includes methods of making these articles, along with glass compositions for them. The glass compositions of the disclosure are suitable for co-sagging processes with an SLG ply, e.g., to form automotive and architectural glazing. Viscosity within the co-sagging temperature range can be controlled by selecting particular compositions of the core glass and / or clad glass layers. Various viscosity adjustments can be made within the compositional ranges of the disclosure, particularly given that the glass compositions employed for the laminate articles of the disclosure are not required to be ion-exchangeable glass compositions (e.g., given the compressive residual stresses afforded by the CTE mismatch between the core and clad glass layers). It is also possible to control the viscosity of the laminate glass articles by controlling the thickness ratios of the core and clad glass layers. Still further, embodiments of the core and clad glass compositions are ion-exchangeable, thus facilitating thedevelopment of compressive stress regions obtained through the summation of mechanical and ion exchange processes.

[0036] Referring now to FIG. 1, an exemplary, laminate glass article 10 (e.g., “glass article”) is provided according to an embodiment of the disclosure. The glass article 10 includes a core glass 12 comprising a first major surface 14 and a second major surface 16. A first clad layer 18 is fused to the first major surface 14 and a second clad layer 20 may be fused to the second major surface 16. In some embodiments, the core glass 12, the first clad layer 18, and the second clad layer 20 are formed of a borosilicate glass comprising SiO2 > 74 mol%, B2O3 > 10 mol%, and A12O3 less than 4 mol%.

[0037] With continued reference to FIG. I, in some embodiments, the laminate glass article 10 may be incorporated into an automobile. For example, an automobile windshield, sunroof, side windows, and / or rear windows may comprise the laminate glass article 10. In some embodiments, the laminate glass article 10 may be incorporated in building windows, airplane windows, and other related window-based, mirror-based, or glass-based applications. In this manner, building windows, airplane windows, windows, mirrors, and glass articles may comprise the laminate glass article 10.

[0038] With continued reference still to FIG. I, the core glass 12 may include a core thickness 22 defined between the first and second major surfaces 14, 16. The core glass 12 may further include a core perimeter 24 delimiting both the first and second major surfaces 14, 16. The first clad layer 18 and the second clad layer 20 may each include an interfacing surface 26 facing the core glass 12 and an outer surface 28 facing away from the core glass 12. The first clad layer 18 may define a first clad layer thickness 30 and a first clad layer perimeter 32. The second clad layer 20 may define a second clad layer thickness 34 and a second clad layer perimeter 36. The laminated glass article 10 may define a total thickness 38 characterized by an aggregation of the core thickness 22, the first clad layer thickness 30, and the second clad layer thickness 34 that is greater than about 1.0 mm. For example, the total thickness of the laminated glass article 10 may be greater than 1.5 mm, greater than 2.0 mm, greater than 2.5 mm, greater than 3.0 mm, between 2.0 mm and 3.0 mm, about 2.3 mm, about 2.5 mm, and all thickness values between these thickness values.

[0039] With reference again to the laminate glass article 10 in FIG. I, the core thickness 22 of the core glass 12 may range from about 0.1 mm to about 5 mm, from about 0.1 mm to about 4 mm, from about 0.1 mm to about 3 mm, from about 0.1 mm to about 2.5 mm, from about 0.1 mm to about 2 mm, from about 0. 1 mm to about 1 mm, from about 0.2 mm to about5 mm, from about 0.2 mm to about 4 mm, from about 0.2 mm to about 3 mm, from about 0.2 mm to about 2.9 mm, from about 0.2 mm to about 2.8 mm, from about 0.2 mm to about 2.7 mm, from about 0.2 mm to about 2.6 mm, from about 0.2 mm to about 2.5 mm, from about 0.2 mm to about 2 mm, from about 0.3 mm to about 5 mm, from about 0.3 mm to about 2.5 mm, from about 0.3 mm to about 2 mm, and all thickness values between these thickness levels.

[0040] Still referring to the laminate glass article 10 in FIG. 1, the first and second clad layer thickness 30, 34 may, respectively, range from about 0.01 mm to about 4 mm, from about 0.01 mm to about 3 mm, from about 0.01 mm to about 2.5 mm, from about 0.01 mm to about 2 mm, from about 0.05 mm to about 3 mm, from about 0.05 mm to about 2.5 mm, from about 0.05 mm to about 2.0 mm, from about 0.05 mm to about 1.5 mm, from about 0.05 mm to about 1 mm, from about 0.05 mm to about 0.5 mm, from about 0.05 mm to about 0.4 mm, from about 0.05 mm to about 0.3 mm, from about 0.05 mm to about 0.2 mm, from about 0.05 mm to about 0.1 mm, from about 0.1 mm to about 3 mm, from about 0.1 mm to about 2.5 mm, from about 0.1 mm to about 2 mm, from about 0.2 mm to about 3 mm, from about 0.2 mm to about 2.5 mm, from about 0.2 mm to about 2 mm, from about 0.3 mm to about 3 mm, from about 0.3 mm to about 2.5 mm, from about 0.3 mm to about 2 mm, and all thickness values between these thickness levels.

[0041] Referring yet again to the laminate glass article 10 in FIG. I, according to some embodiments, a ratio of the core thickness 22 of the core glass layer 12 to the sum of the thicknesses 30 and 34 of the first and second clad layers 18, 20 can range from about 0.5 to about 30, from about 0.5 to about 20, from about 1 to about 20, from about 1 to about 10, or from about 1 to about 7. In some implementations of the laminate glass article 10 depicted in FIG. I, the ratio of the core thickness 22 of the core glass layer 12 to the sum of the thicknesses 30 and 34 of the first and second clad layers 18, 20 can be about 0.5, 0.75, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, and all ratios between these core-to-clad ratio levels. In some embodiments, the clad thickness 30, 34 is equal to a total thickness divided by (2K+2) wherein K is the thickness ratio. In some embodiments, the core thickness 22 is equal to a multiple of 2 of the clad thickness 30, 34 subtracted from the total thickness of the laminate glass article 10.

[0042] In some embodiments, the core glass 12 of the laminate glass article 10 depicted in FIG. 1 can include a relatively high coefficient of thermal expansion (“CTE”) and the first and second clad layers 18, 20 can include a relatively low CTE. The relatively low CTE ofthe first and second clad glass layers 18, 20 can be laminated to the relatively high CTE core glass 12 by bonding the surfaces of the layers together at elevated temperatures such that the first and second clad glass layers 18, 20 are fused to the core glass 12. The laminate glass article 10 is then allowed to cool. As the laminate glass article 10 cools, the relatively high CTE core glass 12 contracts more than the plurality of relatively low CTE of the first and second clad glass layers 18, 20 that are securely bonded to the surfaces of the core glass 12. Due to the variable contraction of the core glass 12 and the first and second clad glass layers 18, 20 during cooling, the core glass 12 is placed in a state of tension (or tensile stress) and the clad glass layers 18, 20 are placed in a state of compression (or compressive stress). This results in a mechanically strengthened, laminate glass article 10 having a stress profile in which the compressive stress (“CS”) extends entirely through the laminate glass article 10. An advantageous compressive stress region is thus formed in the laminate glass article 10 and an advantageous tensile stress is imparted on the core glass 12. In some embodiments, the tensile stress (“TS”) of the core glass 12 is less than about 10 MPa resulting in the laminate glass article 10 exhibiting lower crack propagation in conjunction with high damage resistance. For example, the TS of the core glass 12 may be between about 1 MPa and about 10 MPa, between about 2 MPa and about 10 MPa, between about 3 MPa and about 10 MPa, between about 4 MPa and about 10 MPa, between about 5 MPa and about 10 MPa, between about 6 MPa and about 10 MPa, between about 7 MPa and about 10 MPa, between about 8 MPa and about 10 MPa, between about 9 MPa and about 10 MPa, less than about 15 MPa, less than about 10 MPa, less than about 9 MPa, less than about 8 MPa, less than about 7 MPa, less than about 6 MPa, less than about 5 MPa, less than about 4 MPa, less than about 3 MPa, less than about 2 MPa, less than about 1 MPa, and all TS values between these ranges and values.

[0043] The laminate glass article 10 depicted in FIG. 1 provides strengthening by utilizing the CTE mismatch where the CTE of the core glass 12 is higher than the CTE of the first and second clad layers 18, 20 to CS in the first and second clad layers 18, 20 and CT in the core glass 12. When a flaw depth is smaller than the thickness of the first and second clad layers 18, 20, the compression in the first and second clad layers 18, 20 helps to prevent cracks from propagating. Various core / clad pairs may be utilized with small CTE mismatch to generate CT less than about 10 MPa, therefore even if a crack penetrates the first and second clad layers 18, 20 and reaches the core glass 12, the crack does not have sufficient driving force to overcome the CT in the core glass 12 and self-propagate. The mismatch of CTE on laminateglass article 10 can generate stress on the glass core 12. The double fusion setup (FIG. 2) is one example process to fusion draw the laminate glass article 10. The CTE mismatch between the first and second clad layers 18, 20 and the core glass 12 is large enough to generate meaningful level of CS on the first and second clad layers 18, 20, yet small enough to keep the CT low (e.g., below 10 MPa). As will be described in more detail below, CT levels less than 10 MPa do not result in self-propagation of cracks that enter the core glass 12 (e.g., CT region).

[0044] The CS in the first and second clad layers 18, 20 (ociad) and the CT in the core glass 12 (ocore) are due to the CTE differences between the core glass 12 and the first and second clad layers 18, 20 can be approximated with the following equation:

[0045] With continued reference to the laminate glass article 10 depicted in FIG. I, aciad and aCOre are the coefficient of thermal expansion for the core glass 12 and the first and second clad layers 18, 20 from room temperature (e.g., 25 °C) to the temperature corresponding to a viscosity of 1011Poise (the temperature used for a viscosity of I011. The Poise is typically different for the core glass 12 and first and second clad layers 18, 20, so in this case of the lower of the two values is used. ECOre and Eciad is measured Young’s modulus of the core glass 12 and the first and second clad layers 18, 20, where vCOre andvciad is the Poisson’s ratio of the core glass 12 and the first and second clad layers 18, 20, and k is thickness ratio of core glass 12 to the first and second clad layers 18, 20 as depicted in equation (3) below., > ^coreZtclad ( ) tcore is thickness of core glass 12, and tciad is thickness of single first and second clad layers 18, 20. Using equations (1) - (3) the laminate glass article 10 is formed with with CS >10MPa through the whole first and second clad layers 18, 20 and with the core glass 12 exhibiting CT < 10 MPa.

[0046] With continued reference to the laminate glass article 10 depicted in FIG. 1, the laminate glass article 10 may have one, two or more, or each of various attributes. For example, in some embodiments, the core glass 12 and the first and second clad layers 18, 20 may be formed of a material selected from the borosilicate glass family (including borofusion glasses) such that they have high inherent damage resistance against sharp contact. In some embodiments, a laminate fusion process (FIG. 2) is used to impart a compressive stress over the already damage resistant borofusion family glass. In some embodiments, the stress imparted by lamination is intentionally limited such that the CT level is less than 10 MPa, so the glass core 12 (e.g., and the first and second clad layers 18, 20) is resistant to selfpropagation of cracks that enter the CT region. In some embodiments, the low reforming temperatures (reforming temperatures are estimated as the temperature at 1011Poise) of between about 620° C to 650° C, for example, between about 630° C to 640° C for both the first and second clad layers 18, 20 facilitate the laminate glass article 10 to be used as a drop- in solution for windshield glass production.

[0047] With reference now to FIG. 2, one exemplary embodiment of a laminate overflow distributor apparatus 200 can be used to form the laminate glass article 10 depicted in FIG. 1 using a fusion-draw process. The apparatus 200 is configured generally as described in U.S. Patent No. 4,214,886, which is incorporated by reference herein in its entirety. The apparatus 200 comprises a lower overflow distributor 220 positioned beneath an upper overflow distributor 240. Lower overflow distributor 220 comprises a trough 222. A first glass composition 224 (e.g., the glass composition of the core glass 12) is melted and fed into trough 222 in a viscous state. First glass composition 224 forms the core glass 12 of the laminate glass article 10. Upper overflow distributor 240 comprises a trough 242. A second glass composition 244 (e.g., the glass composition of the first and second clad glass layers 18, 20) is melted and fed into trough 242 in a viscous state. Second glass composition 244 forms the first and second clad glass layers 18 and 20 of the laminate glass article 10.

[0048] With continued reference to the laminate overflow distributor apparatus 200 depicted in FIG. 2, the first glass composition 224 overflows trough 222 and flows down opposing outer forming surfaces 226 and 228 of lower overflow distributor 220. Outer forming surfaces 226 and 228 converge at a draw line 230. The separate streams of first glass composition 224 flowing down respective outer forming surfaces 226 and 228 of loweroverflow distributor 220 converge at draw line 230 where they are fused together to form the core glass 12 of the laminate glass article 10. The second glass composition 244 overflows trough 242 and flows down opposing outer forming surfaces 246 and 248 of upper overflow distributor 240. Second glass composition 244 is deflected outward by upper overflow distributor 240 such that the second glass composition flows around lower overflow distributor 220 and contacts first glass composition 224 flowing over outer forming surfaces 226 and 228 of the lower overflow distributor. The separate streams of second glass composition 244 are fused to the respective separate streams of first glass composition 224 flowing down respective outer forming surfaces 226 and 228 of lower overflow distributor 220. Upon convergence of the streams of first glass composition 224 at draw line 230, second glass composition 244 forms the clad glass layers 18 and 20 of the laminate glass article 10.

[0049] In some embodiments, the laminate glass article 10 is part of a glass sheet traveling away from draw line 230 of lower overflow distributor 220, as shown in FIG. 2. The glass sheet is severed to separate the laminated glass article 10 therefrom. Thus, several laminated glass articles in addition to the laminated glass article 10 can be cut from the glass sheet produced from the laminate overflow distributor apparatus 200 depicted in FIG. 2. The glass sheet can be severed using a suitable technique such as, for example, scoring, bending, thermally shocking, and / or laser cutting.

[0050] Although the laminate glass article 10 depicted in FIG. 1 comprises three layers, however, it should be appreciated that other embodiments are included in this disclosure. In other embodiments, the laminate glass article 10 can have a number of layers, such as two, four, or more layers, that are not otherwise depicted in FIG. 1. For example, one of the first clad layer 18 or the second clad layer 20 can be omitted such that the laminate glass article 10 comprises a two-layer glass sheet consisting of a core glass 12 and one of the clad glass layers 18 or 20. A laminated glass article 10 comprising two layers can be formed using two overflow distributors (see, e.g., the laminate overflow distributor apparatus 200 depicted in FIG. 2) positioned so that the two layers are joined while traveling away from the respective draw lines of the overflow distributors or using a single overflow distributor with a divided trough so that two glass compositions flow over opposing outer forming surfaces of the overflow distributor and converge at the draw line of the overflow distributor. Additionally, it should be appreciated that the laminate glass article 10 may comprise four or more layers using additional overflow distributors and / or using overflow distributors with dividedtroughs. Thus, the laminate glass article 10 may have any determined number of layers by modifying the overflow distributor accordingly. In some embodiments, one or more intermediate layers may be disposed between the core glass 12 and the first and / or the second clad glass layer 18 or 20. Thus, the first and second clad glass layers 18 or 20 can be exterior layers regardless of the total number of layers included in the laminated glass article 10.

[0051] With reference now to Table 1 below and FIGS. 3A-8B, the laminate glass article 10 formed of borosilicate glass exhibit advantages over the usage of soda-lime silicate compositions typically used as an exterior windshield ply due to the differences in sharp contact deformation mechanisms. For example, borosilicate glass deforms with more densification when contacted with a Vickers tip when compared to soda-lime silicate glasses. This results in shorter lengths of strength limiting median / radial cracks for a given indentation load due to reduced residual stress surrounding the indent impression. Furthermore, glass compositions that deform with a high degree of densification (e.g., borosilicate glass) tend to form a circular ring crack surrounding the indent impression that extends into the subsurface as a cone-shaped or ring-shaped crack. The cone-shaped or ringshaped crack functions as a terminal boundary to the extension of strength limiting median / radial cracks.

[0052] With reference now to Table 1 and FIGS. 3A and 3B, certain non-limiting examples of compositions and material properties suitable for the clad glass layers 10 and the core glass 12 of the laminate glass article 10 (El) are provided with a comparative example (CE1). With reference now particularly to FIG. 3A, CTE is provided as a function of temperature for the laminate glass article 10 (El) provided Table 1. With reference now particularly to FIG. 3B, CTE is provided as a function of temperature for the comparative example (CE1) provided Table 1.TABLE 1 - Exemplary Glass Compositions and Material Properties for Core glass and Clad layers of the Laminate Article 10 (El) and a Comparative Example (CE1)*The negative sign means the stress is compression.&The CT and CS do not change with glass thickness at a fixed k value.

[0053] With reference now to FIGS. 4-5, a Vickers dart drop test was performed on both the laminate glass article 10 (El) and the comparative example (CE1) provided in Table 1. The Vickers dart drop test utilized a Vickers dart including a weight of 8.5 g. The Vickers dart was formed of diamond and defined a four-sided pyramidal tip having a 136° angle between faces. The Vickers dart drop test was performed by dropping the Vickers dart from incrementally increasing heights until failure was observed. Failure is defined as when the glass surface exhibits any number of radial / median cracks emanating from the comers of the indent impression that are greater than 10 mm in length. With reference now particularly to FIG. 4, the Vickers dart drop test results for El core glass (at 3.3 mm) were compared with other commercial glasses. The laminated example El (at 2.5 mm) shows superior results in this test with three out of seven glasses surviving up to the standard maximum height of 800 mm. Two prototypes of the laminated example El were further tested up to 1300 mm and they both survived failures. With reference now to FIG. 5, the Vickers dart drop test results on seven examples of El laminate glass (2.5 mm thickness) at target thickness ratio 3.6 areprovided. The bars with patterns indicate suspended data in which the parts do not fail at the maximum height tested, the other specimens (un-pattemed bars) failed at the height indicated. As such, the laminate glass article 10 may be generally defined as including a failure height greater than 500 mm when subjected to the Vickers dart test utilizing the Vickers dart that has a weight of 8.5 g. In this manner, when the Vickers dart test is subjected above the failure height, one or more of the core glass 12, the first clad layer 18, and the second clad layer 20 will exhibit a cone crack. The laminate glass article 10 subjected to the Vickers dart test had a clad thickness 30 of about 0.33 mm of the first clad layer 18, a core thickness 22 of about 1.95 mm, with a total thickness of about 2.5 mm.

[0054] With reference now to FIGS. 6A-6B, a Gravelometer test was performed according to ISO20567-1. The abrasion media is certified crushed granite #6 (e.g., Rib Mountain Colonial Red Granite) with a size between 3 / 16 and A inches (i.e., between 4.8 and 12.7mm). The abrasion surface is masked with a center opening at 1.625” diameter. An abrasion pressure was measured at 30 Psi, with the sample glass placed against a rigid steel plate. The Gravelometer test results from 2.1 mm soda-lime (CE1) and 2.3 mm of the laminate glass article 10 (El) from Table 1 are provided in FIGS. 6A and 6B. All tested soda-lime glass samples exhibited massive cracks, meanwhile, the laminate glass article 10 (El) only exhibited minor chips. In this manner, when the Gravelometer failure test is subjected, one or more of the core glass 12, the first clad layer 18, and the second clad layer 20 will exhibit an isolated chip contained entirely within a perimeter of the glass article 10. The laminate glass article 10 subjected to the Gravelometer test had a clad thickness 30 of about 0.25 mm of the first clad layer 18, a core thickness 22 of about 1.8 mm, with a total thickness of about 2.3 mm. In FIG. 6A, the sample glass included four pieces of soda- lime at 2.1 mm thickness and a 6 inch by 6 inch perimeter. In FIG. 6B, the sample glass included five pieces of soda-lime at 2.3 mm thickness and a 2 inch by 2 inch perimeter.

[0055] With reference now to FIGS. 7A and 7B, a poke test was also performed on the soda-lime (CE1) and the laminate glass article 10 (El) from Table 1. The poke test shows how the cracks, which reached the core glass 12 of the laminate glass article 10 (El) are prevented from propagating. The poke test was performed by placing a flat sample laminate (i.e., El and CE1) on a steel platform. A tungsten carbide scribe tip was slowly pressed into the glass by 0.5 pm increments by moving the micrometer dial. Once the tip moves into a core layer (i.e., the core 12 or the core of CE1), a light popping sound was heard. The results of the poke test show that the cracks in the core of the comparative example (CE1) extendedrapidly, while cracks in the core glass 12 of the laminate glass article 10 (El) did not propagate with time. More particularly, FIG. 7A illustrates crack propagation over time in the core of the comparative example (CE1) and FIG. 7B illustrates crack propagation over time in the core glass 12 of the laminate glass article 10 (El). From left-to-right, the images in FIGS. 7A and 7B were taken right after the poke test, 10 minutes after the poke test, 2 hours after the poke test, and 19 hours after the poke test, respectively. As best illustrated in FIG. 8A, a microscopy image taken two days after the poke test shows crack propagation in the core of the comparative example (CE1). FIG. 8B, on the other hand, illustrates a microscopy image taken two days after the poke test shows there is no extension of median / radial cracks in the core glass 12 of the laminate glass article 10 (El). The laminate glass article 10 subjected to the poke test had a clad thickness 30 of about 0.25 mm of the first clad layer 18, a core thickness 22 of about 1.8 mm, with a total thickness of about 2.3 mm.

[0056] With reference back to FIGS. 1-8B, the core glass 12, the first clad layer 18, and the second clad layer 20 may be formed of a borosilicate glass comprising SiCh > 74 mol%, B2O3 > 10 mol%, and AI2O3 less than 4 mol%. In some embodiments, the core glass 12, the first clad layer 18, and the second clad layer 20 further comprise a balance of P2O5, R2O, and RO. In some embodiments, R is selected from a group comprising at least one of Li, Na, K, Sr, and Cs. In some embodiments, R is selected from a group comprising at least one of Mg, Zn, Ca, Sr, and Ba. The CTE of the core glass 12 is higher than the CTE of the first and second clad layers 18, 20. The borosilicate glass composition used for forming the core glass 12 and first and second clad layers will form cone cracks during Vickers indentation. The borosilicate glass composition includes a compressive stress on the first and second clad glass layers 18, 20 and a tensile stress on the core glass 12. The tensile stress on the core glass 12 is limited to less than 10 MPa to reduce the propensity towards self-propagation of cracks. The borosilicate glass compositions exhibit low reforming temperatures (reforming temperatures are estimated as the temperature at 1011Poise) of 630° to 640°C for both core glass 12 and the first and second clad layer 18, 20 compositions to enable the laminate glass article 10 to be used as a drop-in solution for windshield glass production. The the laminate glass article 10 may have a total thickness of 2.3 mm (TR = 3.6) and does not fail when subjected to the Gravelometer test conditions described above. The laminate glass article 10 may have a total thickness of 2.5 mm (TR = 3.6) and provides a failure height greater than 500 mm when subjected to the Vickers dart test described above.

[0057] The disclosure is further summarized in the following paragraphs and is further characterized by combinations of any and all of the various aspects described therein.

[0058] According to one embodiment, a glass article includes a core glass comprising a first major surface and a second major surface. A first clad layer is fused to the first major surface and a second clad layer is fused to the second major surface. The core glass, the first clad layer, and the second clad layer are formed of a borosilicate glass comprising SiO2 > 74 mol%, B2O3 > 10 mol%, and A12O3 less than 4 mol%.

[0059] According to one aspect, a core glass, a first clad layer, and a second clad layer further comprise a balance of P2O5, R2O, and RO.

[0060] According to another aspect, R is selected from a group comprising at least one of Li, Na, K, Sr, and Cs.

[0061] According to yet another aspect, R is selected from a group comprising at least one of Mg, Zn, Ca, Sr, and Ba.

[0062] According to still yet another aspect, a core glass has a first coefficient of thermal expansion (CTE) and first and second clad layers have a second CTE that is less than the first CTE.

[0063] According to one aspect, first and second clad layers have a compressive stress that imparts a tensile stress on a core glass.

[0064] According to another aspect, a tensile stress on a core glass is less than 10 MPa to reduce a propensity towards self-propagation of cracks.

[0065] According to yet another aspect, a core glass, a first clad layer, and a second clad layer have reforming temperatures between 620° C and 650° C.

[0066] According to still yet another aspect, an automobile windshield comprises a glass article.

[0067] According to one aspect, a glass article includes a failure height greater than 500 mm when subjected to a Vickers dart test, the Vickers dart test includes utilizing a Vickers dart that has a weight of 8.5 g.

[0068] According to another aspect, when a Vickers dart test is subjected above a failure height on a glass article, one or more of a core glass, a first clad layer, and a second clad layer exhibit a cone crack.

[0069] According to yet another aspect, when a Gravelometer failure test with an abrasion pressure of 30 psi is subjected to a glass article, one or more of a core glass, a first clad layer,and a second clad layer will exhibit an isolated chip contained entirely within a perimeter of the glass article.

[0070] According to another embodiment, a glass article includes a core glass formed of a borosilicate glass that comprises a first major surface and a second major surface. The core glass has a first coefficient of thermal expansion (CTE). A first clad layer is fused to the first major surface and a second clad layer is fused to the second major surface. The first clad layer and the second clad layer are formed of a borosilicate glass and have a second CTE that is less than the first CTE. The first and second clad layers have a compressive stress that imparts a tensile stress on the core glass of less than 10 MPa.

[0071] According to one aspect, a core glass, a first clad layer, and a second clad layer are formed of a borosilicate glass, a borosilicate glass comprising SiCL > 74 mol%, B2O3 > 10 mol%, and AI2O3 less than 4 mol%.

[0072] According to another aspect, a core glass, a first clad layer, and a second clad layer further comprise a balance of P2O5, R2O, and RO.

[0073] According to yet another aspect, R is selected from a group comprising at least one of Li, Na, K, Sr, and Cs and / or R is selected from a group comprising at least one of Mg, Zn, Ca, Sr, and Ba.

[0074] According to still yet another aspect, a glass article exhibits a failure height greater than 500 mm when subjected to a Vickers dart test. The Vickers dart test includes utilizing a Vickers dart that has a weight of 8.5 g, and when the Vickers dart test is subjected above a failure height, one or more of a core glass, a first clad layer, and a second clad layer of the glass article will exhibit a cone crack.

[0075] According to yet another embodiment, a glass article includes a core glass comprising a first major surface and a second major surface. The core glass has a first coefficient of thermal expansion (CTE). A first clad layer is fused to the first major surface and a second clad layer is fused to the second major surface. The first clad layer and the second clad layer have a second CTE that is less than the first CTE. The glass article further includes a failure height greater than 500 mm when subjected to a Vickers dart test. The Vickers dart test includes utilizing a Vickers dart that has a weight of 8.5 g. When the Vickers dart test is subjected above the failure height, one or more of the core glass, the first clad layer, and the second clad layer will exhibit a cone crack.

[0076] According to one aspect, a first and second clad layers have a compressive stress that imparts a tensile stress on a core glass less than 10 MPa.

[0077] According to another aspect, a first clad layer, and a second clad layer are formed of a borosilicate glass comprising SiCh > 74 mol%, B2O3 > 10 mol%, and AI2O3 less than 4 mol%.

[0078] While exemplary embodiments and examples have been set forth for the purpose of illustration, the foregoing description is not intended in any way to limit the scope of disclosure and appended claims. Accordingly, variations and modifications may be made to the above-described embodiments and examples without departing substantially from the spirit and various principles of the disclosure. All such modifications and variations are intended to be included herein within the scope of this disclosure and protected by the following claims.

Claims

What is claimed is:

1. A glass article, comprising: a core glass comprising a first major surface and a second major surface; a first clad layer fused to the first major surface; a second clad layer fused to the second major surface; and wherein the core glass, the first clad layer, and the second clad layer are formed of a borosilicate glass comprising SiCfi > 74 mol%, B2O3 > 10 mol%, and AI2O3 less than 4 mol%.

2. The glass article of claim 1, wherein the core glass, the first clad layer, and the second clad layer further comprise a balance of P2O5, R2O, and RO.

3. The glass article of claim 2, wherein R is selected from a group comprising at least one of Li, Na, K, Sr, and Cs.

4. The glass article of claim 3, wherein R is selected from a group comprising at least one of Mg, Zn, Ca, Sr, and Ba.

5. The glass article of claim 1, wherein the core glass has a first coefficient of thermal expansion (CTE) and the first and second clad layers have a second CTE that is less than the first CTE.

6. The glass article of claim 5, wherein the first and second clad layers have a compressive stress that imparts a tensile stress on the core glass.

7. The glass article of claim 6, wherein the tensile stress on the core glass is less than 10 MPa to reduce a propensity towards self-propagation of cracks.

8. The glass article of claim 1, wherein the core glass, the first clad layer, and the second clad layer have reforming temperatures between 620° C and 650° C.

9. An automobile windshield comprising the glass article of claim 8.

10. The glass article of claim 1, further including a failure height greater than 500 mm when subjected to a Vickers dart test, wherein the Vickers dart test includes utilizing a Vickers dart that has a weight of 8.5 g.

11. The glass article of claim 10, wherein when the Vickers dart test is subjected above the failure height, one or more of the core glass, the first clad layer, and the second clad layer will exhibit a cone crack.

12. The glass article of claim 11, further including a Gravelometer failure test with an abrasion pressure of 30 psi, wherein when the Gravelometer failure test is subjected, one or more of the core glass, the first clad layer, and the second clad layer will exhibit an isolated chip contained entirely within a perimeter of the glass article.

13. A glass article, comprising: a core glass formed of a borosilicate glass and comprising a first major surface and a second major surface, the core glass having a first coefficient of thermal expansion (CTE); a first clad layer fused to the first major surface and a second clad layer fused to the second major surface, the first clad layer and the second clad layer formed of a borosilicate glass and having a second CTE that is less than the first CTE; and wherein the first and second clad layers have a compressive stress that imparts a tensile stress on the core glass less than 10 MPa.

14. The glass article of claim 13, wherein the core glass, the first clad layer, and the second clad layer are formed of the borosilicate glass, the borosilicate glass comprising SiCh > 74 mol%, B2O3 > 10 mol%, and AI2O3 less than 4 mol%.

15. The glass article of claim 14, wherein the core glass, the first clad layer, and the second clad layer further comprise a balance of P2O5, R2O, and RO.

16. The glass article of claim 15, wherein R is selected from a group comprising at least one of Li, Na, K, Sr, and Cs or from a group comprising at least one of Mg, Zn, Ca, Sr, and Ba.

17. The glass article of claim 13, further including a failure height greater than 500 mm when subjected to a Vickers dart test, wherein the Vickers dart test includes utilizing a Vickers dart that has a weight of 8.5 g, and when the Vickers dart test is subjected above the failure height, one or more of the core glass, the first clad layer, and the second clad layer will exhibit a cone crack.

18. A glass article, comprising: a core glass comprising a first major surface and a second major surface, the core glass having a first coefficient of thermal expansion (CTE); a first clad layer fused to the first major surface and a second clad layer fused to the second major surface, the first clad layer and the second clad layer having a second CTE that is less than the first CTE; and a failure height greater than 500 mm when subjected to a Vickers dart test, wherein the Vickers dart test includes utilizing a Vickers dart that has a weight of 8.5 g, and when the Vickers dart test is subjected above the failure height, one or more of the core glass, the first clad layer, and the second clad layer will exhibit a cone crack.

19. The glass article of claim 18, wherein the first and second clad layers have a compressive stress that imparts a tensile stress on the core glass less than 10 MPa.

20. The glass article of claim 19, wherein the core glass, the first clad layer, and the second clad layer are formed of a borosilicate glass comprising SiCh > 74 mol%, B2O3 > 10 mol%, and AI2O3 less than 4 mol%.

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