Method for controlling bow in laminate structure

Abstract

A method of controlling or changing a bow or curvature in laminated glass structures includes heating a thermoplastic polymer of a laminated glass structure having an initial curvature. A force is utilized to change the curvature, and the laminated structure is cooled to harden the thermoplastic polymer, upon cooling, whereby the laminated glass structure has a curvature that is different than the initial curvature.

Description

METHOD FOR CONTROLLING BOW IN LAMINATE STRUCTURECROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of priority under 35 U.S.C. § 119 of U.S. Provisional Application No. 63 / 568,797 filed March 22, 2024, the content of which is incorporated herein by reference in its entirety.TECHNICAL FIELD

[0002] The present invention generally relates to glass laminates having outer sheets of material with different coefficients of thermal expansion that may result in bowing.BACKGROUND

[0003] Laminate structures may be used for a wide range of applications in a variety of industries. For example, laminate structures may be used in architectural applications such as siding, decorative panels, cabinet installations, wall coverings, and the like. Laminate structures may also be used for furniture items and / or household appliances. For instance, laminate structures may be incorporated as outer panels for a cabinet, furniture item, and / or household appliance.

[0004] Automotive, transportation, aviation, and architectural windows are often made from laminate structures comprising two glass sheets of similar thickness and composition. However, for various applications it may be desirable to provide laminate structures comprising dissimilar substrates, e.g., substrates of different composition and / or thickness. For instance, metal-glass laminates, plastic-glass laminates, glass-ceramic laminates, and other similar laminates may be desirable for aesthetic or structural qualities.

[0005] In addition, glass-glass laminates comprising dissimilar glass substrates may also be desirable for various applications, for example, laminates comprising glasses having different compositions, thicknesses, and / or other properties such as coefficient of thermal expansion (CTE). By way of a non-limiting example, a thin sheet of ion-exchanged glass may be laminated on a thicker soda lime glass sheet to provide enhanced damage resistance.Electrochromic windows and mirrors may comprise a thin, alkali-free glass substrate upon which an electrically active thin film is deposited, which may be laminated to a thicker soda lime glass substrate for enhanced structural rigidity.SUMMARY

[0006] According to aspect (1), a method of forming a laminated sheet of glass is provided. The method comprises: positioning thermoplastic polymer material between first and second layers of glass to form a stack. The first layer of glass comprises a first glass material having a first coefficient of thermal expansion (CTE), and the second layer of glass comprises a second glass material having a second CTE, wherein the second CTE is greater than the first CTE. The polymer material is heated to a lamination temperature to soften the thermoplastic polymer material to form a stack structure. The stack structure is cooled whereby the thermoplastic polymer material hardens and forms a first sheet structure having a first curvature. The first curvature results from a difference between the first CTE and the second CTE. This is followed by heating the first sheet structure to soften the thermoplastic polymer material. The method further includes utilizing a force to change a shape of the first sheet structure while the thermoplastic polymer material is softened to thereby form a second sheet structure. The second sheet structure is cooled, whereby the thermoplastic polymer material hardens to form a laminated sheet of glass having a second curvature that is not identical to the first curvature.

[0007] According to aspect (2), the method of aspect (1) is provided, wherein: at least a portion of the first sheet structure has a convex curvature, at least a portion of a second side of the first sheet structure has a concave curvature, and utilizing a force to change a shape of the first sheet structure includes applying pressure to a first side of the first sheet structure.

[0008] According to aspect (3), the method of aspect (2) is provided, wherein: the pressure applied to the first side of the first sheet structure is greater than a pressure applied to the second side of the first sheet structure.

[0009] According to aspect (4), the method of aspect (3) is provided, wherein: the pressure applied to the second side of the first sheet structure comprises atmospheric pressure.

[0010] According to aspect (5), the method of aspect (3) is provided, wherein: pressure is applied to the first side of the first sheet structure while the first sheet structure is in an oven.

[0011] According to aspect (6), the method of aspect (1) is provided, wherein: at least a portion of the first sheet structure has a convex curvature, and at least a portion of a secondside of the first sheet structure has a concave curvature; and utilizing a force to change a shape of the first sheet structure comprises supporting the first sheet structure with the first side of the first sheet structure facing upwardly while the thermoplastic polymer material is soft, whereby gravity acting on the first sheet structure reduces the curvature of the first sheet structure before the first sheet structure is cooled to harden the thermoplastic polymer material.

[0012] According to aspect (7), the method of aspect (6) is provided, wherein: the first sheet structure has a quadrilateral perimeter with four corners; and the first sheet structure is supported at each comer while the first sheet structure is cooled to harden the thermoplastic polymer material.

[0013] According to aspect (8), the method of aspect (1) is provided, wherein: the second CTE is at least twice the first CTE; and the first layer of glass is thinner than the second layer of glass.

[0014] According to aspect (9), the method of aspect (8) is provided, wherein: the second layer of glass is at least five times as thick as the first layer of glass.

[0015] According to aspect (10), the method of aspect (9) is provided, wherein: the first glass material comprises an alkaline earth boro-aluminosilicate glass; the second glass material comprises soda lime glass; and the thermoplastic polymer material comprises a layer of polyvinyl butyral.

[0016] According to aspect (11), the method of aspect (10) is provided, wherein: the first layer of glass is 0.7 mm thick; the second layer of glass is 5 mm thick; and the layer of thermoplastic polymer material is 2.3 mm thick.

[0017] According to aspect (12), a method of reducing bow of a laminated sheet of glass comprising thermoplastic polymer material between first and second layers of glass is provided. The method comprise: heating the laminated sheet of glass to soften the thermoplastic polymer material; utilizing a force to reduce the bow of the laminated sheet of glass while the thermoplastic polymer material is softened; cooling the laminated sheet of glass whereby the thermoplastic polymer material hardens and the bow of the laminated sheet of glass is reduced.

[0018] According to aspect (13), the method of aspect (12) is provided, wherein: the first layer of glass comprises a first glass material having a first coefficient of thermal expansion (CTE), and the second layer of glass comprises a second glass material having a second CTE, wherein the second CTE is greater than the first CTE.

[0019] According to aspect (14), the method of aspect (12) is provided, wherein: at least a portion of a first side the laminated sheet of glass initially has a convex curvature, and at least a portion of a second side of the laminated sheet of glass has a concave curvature; and including: applying pressure to the first side of the laminated sheet of glass.

[0020] According to aspect (15), the method of aspect (14) is provided, wherein: at least a portion of a side of the laminated sheet of glass has a convex curvature, and at least a portion of a second side of the laminated sheet of glass has a concave curvature; and utilizing a force to reduce the bow of the laminated sheet of glass comprises supporting the laminated sheet of glass with the first side of the laminated sheet of glass thereof facing upwardly while the thermoplastic polymer material is soft, whereby gravity acting on the laminated sheet of glass reduces the bow of the laminated sheet of glass before the laminated sheet of glass is cooled.

[0021] According to aspect (16), the method of aspect (15) is provided, wherein: the laminated sheet of glass has a quadrilateral perimeter with four corners; and the laminated sheet of glass is supported at each corner while the laminated sheet of glass is cooled to harden the thermoplastic polymer material.

[0022] According to aspect (17), the method of aspect (15) is provided, wherein: the laminated sheet of glass is positioned on a flat surface while the laminated sheet of glass is cooled to harden the thermoplastic polymer material.

[0023] According to aspect (18), the method of aspect (13) is provided, wherein: the second CTE is at least twice the first CTE; the first layer of glass is thinner than the second layer of glass.

[0024] According to aspect (19), the method of aspect (18) is provided, wherein: the second layer of glass is at least five times as thick as the first layer of glass.

[0025] According to aspect (20), the method of aspect (19) is provided, wherein: the first glass material comprises an alkaline earth boro-aluminosilicate glass; the second glass material comprises soda lime glass; and the thermoplastic polymer material comprises a layer of polyvinyl butyral.

[0026] According to aspect (21), the method of any one of aspects (12) to (20) is provided, further comprising: stacking the laminated sheet of glass and one or more further laminated sheets of glass (one by one) to form a stack of laminated sheets of glass before the heating, each of the one or more further laminated sheets of configured in substantially the same manner as the laminated sheet of glass, wherein the stack of laminated sheets of glass is heated to soften the thermoplastic polymer material in each of the laminated sheet of glassand the one or more further laminated sheets of glass, wherein the force is utilized on the stack of laminated sheets of glass to reduce the bow of each of the laminated sheet of glass and the one or more further laminated sheets of glass while the thermoplastic polymer material is softened, and wherein the stack of laminated sheets of glass is cooled so as to harden the thermoplastic polymer material and reduce the bow of each of the laminated sheet of glass and the one or more further laminated sheets of glass.

[0027] 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.

[0028] 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. The accompanying drawings are included to provide a further understanding, and are incorporated in and constitute a part of this specification. The drawings illustrate one or more embodiments, and together with the description serve to explain principles and operation of the various embodiments.BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In the drawings:

[0030] FIG. l is a partially schematic cross-sectional view of a laminate structure according to an aspect of the present disclosure;

[0031] FIG. 2 is a partially schematic cross-sectional view of the laminate structure of FIG. 1 showing expansion of the layers due to changes in temperature;

[0032] FIG. 3 is a partially schematic cross-sectional view of a laminate structure that is bowed upon cooling; and

[0033] FIG. 4 is a graph showing long edge bow of a laminated glass structure as a function of the glass diagonal dimension.DETAILED DESCRIPTION

[0034] In the following detailed description, for purposes of explanation and not limitation, example embodiments disclosing specific details are set forth to provide a thoroughunderstanding of various principles of the present disclosure. However, it will be apparent to one having ordinary skill in the art, having had the benefit of the present disclosure, that the present disclosure may be practiced in other embodiments that depart from the specific details disclosed herein. Moreover, descriptions of well-known devices, methods and materials may be omitted so as not to obscure the description of various principles of the present disclosure. Finally, wherever applicable, like reference numerals refer to like elements.

[0035] Ranges can be expressed herein as from “about” one particular value, and / or to “about” another particular value. 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 endpoint of a range, the disclosure should be understood to include the specific value or endpoint referred to. Whether or not a numerical value or endpoint of a range in the specification recites “about,” the numerical value or endpoint 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 endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint.

[0036] 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, for example within about 5% of each other, or within about 2% of each other.

[0037] As used herein, the term “dispose” includes coating, depositing and / or forming a material onto a surface. The disposed material may constitute a layer, as defined herein. The phrase “disposed on” includes the instance of forming a material onto a surface such that the material is in direct contact with the surface and also includes the instance where the material is formed on a surface, with one or more intervening material(s) between the disposed material and the surface. The intervening material(s) may constitute a layer, as defined herein.

[0038] 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 / or to any specific orientation described herein and are not intended to imply absolute orientation.

[0039] Unless otherwise expressly stated, it is in no way intended that any method set forth herein be construed as requiring that its steps be performed in a specific order. Accordingly, where a method claim does not actually recite an order to be followed by its steps, or it is not otherwise specifically stated in the claims or descriptions that the steps are to be limited to a specific order, it is in no way intended that an order be inferred, in any respect. This holds for any possible non-express basis for interpretation, including: matters of logic with respect to arrangement of steps or operational flow; plain meaning derived from grammatical organization or punctuation; the number or type of embodiments described in the specification.

[0040] As used herein, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to a “component” includes embodiments having two or more such components, unless the context clearly indicates otherwise.

[0041] Laminate structures comprising dissimilar substrates may be referred to herein as "asymmetric" laminates. While asymmetric laminates may present one or more advantages as compared to symmetric laminates, these laminates can also present various challenges. For example, asymmetric laminates can comprise two or more substrates with different CTEs. During the lamination process, the substrates can be heated to a lamination temperature and subsequently cooled, e.g., to room temperature. When the laminate structure cools, the CTE mismatch between the substrates can lead to out-of-plane deflection (often referred to as "bow"). Bow in laminate structures can interfere with subsequent processing steps such as film deposition, can result in unwanted optical distortion in the final product, and / or can result in a product that is unsuitable for the intended application and / or does not meet the desired target shape.

[0042] With reference to FIG. 1, a laminated structure 1 according to an aspect of the present disclosure includes a first layer of material 2, a second layer of material 3, and a thermoplastic polymer material (“interlayer”) 4 disposed between the first layer 2 and the second layer 3. The first layer 2 may comprise a first glass material having a thickness “Tl” and second layer 3 may comprise a glass material having a second thickness “T2 ” The first thickness Tl may, optionally, be less than the second thickness T2. For example, the first thickness Tl may be 0.7 mm, and the second thickness T2 may be about 5 mm. The polymer interlayer 4 may,optionally, have a thickness “T3” that is between the thickness T1 and T2. For example, the thickness T3 may be about 2.3 mm. However, the present disclosure is not limited to specific thicknesses, and the thicknesses Tl, T2, and T3 may be larger or smaller than the examples noted above as required for a particular application.

[0043] The first layer 2 may, optionally, comprise an Architectural Technical Glass (ATG) such as EAGLE XG® available from Corning Incorporated of Corning NY. More specifically, the material of first layer 2 may comprise an Alkaline Earth Boro-Aluminosilicate. This material may have a coefficient of thermal expansion (CTE) of about 3.2 X 10'6 / K.

[0044] The second glass of second layer 3 may, optionally, comprise a tempered soda lime glass wherein T2 is about 4 mm to about 6 mm, and wherein the glass has a CTE of about 9.2 X 10’6 / K.

[0045] The polymer interlayer 4 may comprise, for example, PVB RA41 or other suitable material. In general, the thickness, softening temperature, melting temperature, and other properties of the polymer interlayer 4 may be selected as required for a particular application.

[0046] With reference to FIG. 2, during fabrication, the polymer interlayer 4 is positioned between the first layer 2 and the second layer 3 to form an intermediate assembly or stack 10. The stack 10 is then heated to soften the polymer interlayer 4, and a force such as pressures Pl and P2 may be applied to upper and lower sides 12 and 14, respectively, of stack 10 to pretreat stack 10. Various suitable pretreatment processes are known in the art. As discussed in more detail below, several hot press operations may be utilized during the fabrication process. Following pretreatment, the stack 10 may be further heated and additional pressure Pl and P2 may be applied in one or more additional hot press steps. Various suitable hot press processes are known in the art. During the hot press operation(s), the first and second layers of glass 2 and 3 expand at different rates as shown by the arrows “El” and “E2 ” It will be understood that FIG. 2 is schematic in nature. At elevated temperatures (e.g. during the hot press operations), the material of polymer interlayer 4 is soft such that minimal shear force is transmitted through polymer interlayer 4 between the first and second layers 2 and 3, respectively.

[0047] With further reference to FIG. 3, following the hot press operations, the stack 10 is allowed to cool. Due to the cooling and differences in CTE between the materials of layers 2 and 3, layers 2 and 3 contract as shown by the arrows “Cl” and “C2 ” As noted above, the material of second layer 3 may have a CTE that is significantly greater than the CTE of the material of first layer 2. Upon cooling, this may result in greater contraction of layer 3compared to layer 2, leading to a bowed initial (first) laminated sheet structure 15 as shown in FIG. 3. The initial (first) laminated sheet 15 has a convex surface 16 and a concave surface 17. As the polymer interlayer 4 cools, shear forces are transferred between layers 2 and 3 leading to the bowed shape of initial laminated sheet 15. It will be understood that the curvature of the initial laminated sheet 15 shown in FIG. 3 is exaggerated, and the actual curvature of initial laminated sheet 15 may be less than the amount shown in FIG. 3.

[0048] In general, differential cooling of stack 10 may reduce or eliminate bow (curvature) as described in U.S. Patent No. 10,189,228, the entire contents of which are incorporated herein by reference. In general, bow may be measured per ASTM Cl 172. However, initial laminated sheet structure 15 may have at least some significant bow. In general, the first (bowed) sheet structure 15 may be formed by various known processes.

[0049] According to an aspect of the present disclosure, the initial (first) laminated sheet structure 15 may be heated to soften the material of the polymer interlayer 4, and a force “F” may then be utilized to reduce the curvature of the laminated sheet structure while the polymer interlayer 4 is soft, and the polymer interlayer 4 may then be cooled while the force F is applied while the polymer interlayer 4 is allowed to cool, thereby reducing the curvature of the initial (first) laminated sheet 15 to form a final (flat) laminated structure 1 (FIG. 1). In general, the force F may comprise a pressure “P3” that is applied to convex surface 16, or the force F may be a gravitational force resulting from the mass of the sheets 2, 3, and 4. One ore more weights such as flat (first) or curved sheets of material (not shown) may also be placed on convex surface 16 while polymer material is soft due to heating, whereby the weights create or increase force F. The laminated sheet structure 15 may, optionally, have a quadrilateral perimeter with four corners, and a support 18 may be positioned at one or more of the corners of the concave lower side 14. Supports 18 support the sheet structure 15 on a surface 20 as the sheet structure 15 is heated to soften polymer interlayer 4. Supports 18 may comprise resilient blocks or other suitable structures. Also, supports 18 may comprise elongated members that extend along opposite edges 22 and 23 of intermediate structure 15. In general, supports may have virtually any size and configuration as required for a particular application.

[0050] As the polymer interlayer 4 is heated and a force F is applied, the sheet structure 15 will begin to deform due to the force F. Depending on the temperature and the amount of force F, the lower side 14 of intermediate structure or sheet 15 may become planar, or it may sag below a plane 24 whereby lower side 14 has a convex shape as shown by the dashed line 17 A. The sheet structure 15 is then allowed to cool (e.g. at room temperature) while the force F is applied.During cooling, the first and second layers 2 and 3 then contract. This contraction may cause the lower side 14 to shift upwardly from the position 17A due to differences in the CTE of layers 2 and 3. The contraction may cause the lower side 14 to shift to a flat position shown by the dashed line 24, whereby a substantially flat final sheet 1 (FIG. 1) is produced.

[0051] While the method described herein can reduce the bow of a single initial laminated sheet 15, the method can also reduce the bow of a plurality of initial laminated sheets 15 at the same time. For example, the method can further comprise stacking the laminated sheet of glass (initial laminated sheet 15) and one or more further laminated sheets of glass (further initial laminated sheets) to form a stack of laminated sheets of glass before the heating (e.g., before the heating step used to soften the thermoplastic polymer material). The one or more further initial laminated sheets (not shown) are each configured in substantially the same manner as the initial laminated sheet such that the initial laminated sheet and the one or more further initial laminated sheets are simply referred to as initial laminated sheets 15. In embodiments, the stacking comprises positioning each pair of adjacent laminated sheets such that the convex surface 16 of one adjacent laminated sheet is against the concave surface 17 of the other adjacent laminated sheet and / or that the concave surface 17 of one adjacent laminated sheet is against the convex surface 16 of the other adjacent laminated sheet. The stack of laminated sheets can include 2, 3, 4, 5, or more initial laminated sheets 15. A material such as talc can be placed between the stacked initial laminated sheets 15 to prevent them from sticking together after the process is completed.

[0052] After stacking the initial laminated sheets 15, the stack of laminated sheets of glass is heated to soften the thermoplastic polymer material in each of the initial laminated sheets 15. After the stack of laminated sheets of glass is heated, the force is utilized on the stack of laminated sheets of glass to reduce the bow of each of the initial laminated sheets 15 while the thermoplastic polymer material is softened. Similar to the initial (first) laminated sheet described with reference to FIGS. 1-3, the stack of laminated sheets of glass will have one exposed side that has a surface with a convex curvature (e.g., exposed convex surface) and an opposite exposed side that has a surface with a concave curvature (e.g., exposed concave surface). The force utilized to reduce the bow of each of the initial laminated sheets 15 in the stack of laminated sheets of glass (e.g., pressure, gravity, weights, etc.) can be applied to or act on the exposed convex surface and / or the exposed concave surface similar to how the force is utilized in connection with the initial (first) laminated sheet described with reference to FIGS. 1-3. After the force is utilized on the stack of laminated sheets of glass, the stack of laminatedsheets of glass is cooled so as to harden the thermoplastic polymer material and reduce the bow of each of the initial laminated sheets 15 and form the final (flat) laminated sheets. The technique of using a stack of initial laminated sheets 15 can increase the throughput of the process.

[0053] Testing was conducted to determine the effects of post-processing heat and force to reduce or eliminate bow. Table 1 shows a test conducted on three samples (PP-1, PP-2, and PP-3) of 36 inch by 60 inch laminated glass.

[0054] Table 1 : Lamination and Post-Process Conditioning of 36” x 60”, 5 mm FTSLG + 0.7 mm ATG 0.76 mm RA41 Laminates

[0055] The “Lamination-Initial” steps may comprise a known lamination process. However, the “Post-Process Conditioning” comprises one or more steps that are believed to be unique.

[0056] In Table 1, “Sag Level” refers to Level 1 / 6 mm = a 14” thick red silicone rubber pad 18 lifting each corner, Level 2 / 10 mm = a 10 mm thick pad 18, and Level 3 / 12 mm = a 14” thick pad 18

[0057] The initial lamination process (top half of Table 1) was conducted utilizing the conditions shown in Table 1, in an autoclave (with the three sample parts in a vertical orientation). Prior to the autoclave initial lamination, the samples were subject to an initial heating process (pretreatment) to reduce the amount of air in the polymer interlayer 4. The initial heating to de-air the laminate prior to positioning the laminates in the autoclave may be done utilizing known processes.

[0058] As shown in Table 1, the post-processing of the initial laminated sheet or structure (e.g. bowed sheet structure 15, FIG. 3) was conducted in an autoclave at about 140° C, at about 180 psi for about 45 minutes. The Post-Process Conditioning of Table 1 was conducted with the laminate in a horizontal position (e.g. FIG. 3), wherein the laminate 15 was supported by blocks 18. As shown in Table 1, the three test samples PP-1, PP-2, and PP-3 were supported on 6 mm,10 mm, and 12 mm blocks 18, respectively, during the post-process conditioning. In general, the post-processing reduced the bow in all three samples, and the third sample (PP-3) had negative bow (corresponding to lower side 14 being below plane 24 in FIG. 3). The three samples of Table 1 had substantially identical sheets of material, and all three samples were initially laminated utilizing the same conditions. Thus, the differences in the final (conditioned) bow may be due to differences in the thicknesses of the supports 18 utilized during the postprocess conditioning. In particular, the results of Table 1 suggest that the lower side of the laminate contacted the support surface (e.g. surface 20, FIG. 3), thereby limiting the amount of depth formation (sag) of the laminate during the post-process conditioning prior to cooling. In general, the thickness of the pads 18 utilized to support the laminate during the post-process conditioning may be adjusted as required to provide a final conditioned sheet structure 1 (FIG. 1) that is planar or approximately planar. For example, referring again to Table 1, the conditioned sample 2 has a positive bow, whereas the conditioned sample 3 has a negative bow. This suggests that blocks 14 having a thickness between 10 mm and 12 mm may result in a final or conditioned bow that is between the bows of the second and third samples PP-2 and PP-3, respectively, shown in Table 1. Thus, testing may be utilized to determine variables such as block thickness that result in a desired (e.g. flat) final shape of laminate. It will be understood that computer modeling may also be utilized to determine a process that results in the desired final shape of the laminate.

[0059] For example, if 12 mm supports 18 are utilized with the laminated sheets of Table 1, the time or temperature of the post-process conditioning could be reduced to thereby reduce the final or conditioned bow. Also, it will be understood that Table 1 represents the results of tests of representative samples having the specific materials, thicknesses, and sizes noted in Table 1. However, the present disclosure is not limited to any specific materials, or sizes, and the present disclosure is also not limited to any specific initial lamination processes, or any specific post-process conditioning. For example, the initial lamination may be performed with the sheets 2, 4, and 6 in a horizontal orientation utilizing commercially available presses having movable upper and lower separately heated platens to laminate the sheets. Also, the postprocess conditioning may be accomplished utilizing an oven or other suitable device to reheat the laminates for post-process conditioning after the initial lamination. Also, the force F (FIG. 3) may be applied utilizing virtually any suitable pressure, tooling, or other means.

[0060] Additional testing on 42 inch by 86 inch asymmetric laminated sheets was also conducted to determine the results of post-processing for larger laminated sheets. This testing involved four test laminates as shown in Table 2.

[0061] Table 2: Initial and Final Bow of 42” x 86” 36” x 60”, 5 mm FTSLG + 0.7 mm ATG 0.76 mm RA41 Laminates

[0062] The sample parts (laminated sheets) of Table 2 include sheets 2, 3, and 4 having substantially the same materials and thicknesses Tl, T2, and T3 in connection with the samples of Table 1. However, the parts (laminates) of Table 2 have a significantly larger perimeter than the parts of Table 1.

[0063] The samples (parts) of Table 2 were subject to the initial lamination process of Table 3.

[0064] Table 3: Initial Lamination of 42” x 86” 36” x 60”, 5 mm FTSLG + 0.7 mm ATG 0.76 mm RA41 Laminates

[0065] The process of Table 3 may be substantially similar to known lamination processes that tend to result in bowed laminates. Known presses may have heated upper and lower platens that are vertically movable within a sleeve extending around the perimeter of the laminate(s) in the press whereby the temperatures and pressures on the upper and lower sides of laminates in the press may be controlled.

[0066] Thus, the top and bottom temperatures of Table 3 represent the temperatures of upper and lower platens of commercially available presses, and the pressures Pl and P2 represent pressures between the upper and lower platens and the upper and lower sides, respectively, of the samples during the initial lamination process. For purposes of testing, the initial lamination process involved two hot presses at the temperatures, pressures, and times listed in Table 3. A final cooling press was also performed as shown in Table 3. The initial lamination process of Table 3 resulted in the initial bow of the parts as shown in Table 2. The process of Table 3 is a representative process that results in bowed laminates. Numerous processes may result in laminates having bow that may be reduced or eliminated utilizing post-processing according to the present disclosure.

[0067] The parts produced by the process of Table 3 were then subject to post-processing as shown in Table 4.

[0068] Table 4: Post-Processing of 42” x 86” 36” x 60”, 5 mm FTSLG + 0.7 mm ATG 0.76 mm RA41 Laminates

[0069] The process of Table 4 did not include a separate cooling press. Rather, the parts (laminated) were positioned / supported on a flat surface to cool at room temperature.

[0070] Referring again to Table 2, the post-processing (Table 4) significantly reduced the final bow of parts 1-4.

[0071] An aspect of the present disclosure is post-processing of asymmetrical glass laminates to reduce or eliminate bow that may result from an initial lamination process. The process (post-processing) may be beneficial if the laminate includes glass materials having different coefficients of thermal expansion that result in bowing of the laminate after the initial laminatefabrication process. In general, the polymer material (interlayer) is allowed to cool during the initial processing, thereby forming a bowed laminate upon cooling of the thermoplastic polymer material of interlayer 4. The bowed laminate is then heated to soften the thermoplastic polymer material of interlayer 4, and pressure or force may be applied while the polymer is softened to thereby reduce or eliminate the bow, and the laminate is again cooled. The laminate may optionally be cooled while the pressure or force is being applied, whereby the polymer interlayer 4 again hardens and forms a final laminate that is flat (planar) or substantially flat. The resulting laminated structure may be utilized in architectural windows for buildings or other such structures.

[0072] The present disclosure is not, however, limited to forming final laminated structures that are planar. For example, if a curved laminate is required for a particular application, the initial lamination process may be utilized to form a laminated structure having an initial curvature. The curved laminate may then be heated, and pressure may be applied to either increase or decrease the curvature as required to form a non-planar final laminate structure having a desired degree of bow or curvature, wherein the final (desired) bow / curvature is nonzero.

[0073] Many variations and modifications may be made to the above-described embodiments / aspects of the disclosure 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 method of forming a laminated sheet of glass, the method comprising: positioning thermoplastic polymer material between first and second layers of glass to form a stack, wherein the first layer of glass comprises a first glass material having a first coefficient of thermal expansion (CTE), and the second layer of glass comprises a second glass material having a second CTE, wherein the second CTE is greater than the first CTE; heating the polymer material to a lamination temperature to soften the thermoplastic polymer material to form a stack structure; cooling the stack structure whereby the thermoplastic polymer material hardens and forms a first sheet structure having a first curvature, wherein the first curvature results from a difference between the first CTE and the second CTE; followed by heating the first sheet structure to soften the thermoplastic polymer material; utilizing a force to change a shape of the first sheet structure while the thermoplastic polymer material is softened to form a second sheet structure; cooling the second sheet structure whereby the thermoplastic polymer material hardens to form a laminated sheet of glass having a second curvature that is not identical to the first curvature.

2. The method of claim 1, wherein: at least a portion of the first sheet structure has a convex curvature, at least a portion of a second side of the first sheet structure has a concave curvature, and utilizing a force to change a shape of the first sheet structure includes applying pressure to a first side of the first sheet structure.

3. The method of claim 2, wherein: the pressure applied to the first side of the first sheet structure is greater than a pressure applied to the second side of the first sheet structure.

4. The method of claim 3, wherein: the pressure applied to the second side of the first sheet structure comprises atmospheric pressure.

5. The method of claim 3, wherein: pressure is applied to the first side of the first sheet structure while the first sheet structure is in an oven.

6. The method of claim 1, wherein: at least a portion of the first sheet structure has a convex curvature, and at least a portion of a second side of the first sheet structure has a concave curvature; and utilizing a force to change a shape of the first sheet structure comprises supporting the first sheet structure with the first side of the first sheet structure facing upwardly while the thermoplastic polymer material is soft, whereby gravity acting on the first sheet structure reduces the curvature of the first sheet structure before the first sheet structure is cooled to harden the thermoplastic polymer material.

7. The method of claim 6, wherein: the first sheet structure has a quadrilateral perimeter with four corners; and the first sheet structure is supported at each comer while the first sheet structure is cooled to harden the thermoplastic polymer material.

8. The method of claim 1, wherein: the second CTE is at least twice the first CTE; and the first layer of glass is thinner than the second layer of glass.

9. The method of claim 8, wherein: the second layer of glass is at least five times as thick as the first layer of glass.

10. The method of claim 9, wherein: the first glass material comprises an alkaline earth boro-aluminosilicate glass; the second glass material comprises soda lime glass; and the thermoplastic polymer material comprises a layer of polyvinyl butyral.

11. The method of claim 10, wherein: the first layer of glass is 0.7 mm thick; the second layer of glass is 5 mm thick; and the layer of thermoplastic polymer material is 2.3 mm thick.

12. A method of reducing bow of a laminated sheet of glass comprising thermoplastic polymer material between first and second layers of glass, the method comprising: heating the laminated sheet of glass to soften the thermoplastic polymer material; utilizing a force to reduce the bow of the laminated sheet of glass while the thermoplastic polymer material is softened; cooling the laminated sheet of glass whereby the thermoplastic polymer material hardens and the bow of the laminated sheet of glass is reduced.

13. The method of claim 12, wherein: the first layer of glass comprises a first glass material having a first coefficient of thermal expansion (CTE), and the second layer of glass comprises a second glass material having a second CTE, wherein the second CTE is greater than the first CTE.

14. The method of claim 12, wherein: at least a portion of a first side the laminated sheet of glass initially has a convex curvature, and at least a portion of a second side of the laminated sheet of glass has a concave curvature; and including: applying pressure to the first side of the laminated sheet of glass.

15. The method of claim 14, wherein: at least a portion of a side of the laminated sheet of glass has a convex curvature, and at least a portion of a second side of the laminated sheet of glass has a concave curvature; and utilizing a force to reduce the bow of the laminated sheet of glass comprises supporting the laminated sheet of glass with the first side of the laminated sheet of glass thereof facing upwardly while the thermoplastic polymer material is soft, whereby gravity acting on the laminated sheet of glass reduces the bow of the laminated sheet of glass before the laminated sheet of glass is cooled.

16. The method of claim 15, wherein: the laminated sheet of glass has a quadrilateral perimeter with four corners; and the laminated sheet of glass is supported at each comer while the laminated sheet of glass is cooled to harden the thermoplastic polymer material.

17. The method of claim 15, wherein: the laminated sheet of glass is positioned on a flat surface while the laminated sheet of glass is cooled to harden the thermoplastic polymer material.

18. The method of claim 13, wherein: the second CTE is at least twice the first CTE; the first layer of glass is thinner than the second layer of glass.

19. The method of claim 18, wherein: the second layer of glass is at least five times as thick as the first layer of glass.

20. The method of claim 19, wherein: the first glass material comprises an alkaline earth boro-aluminosilicate glass; the second glass material comprises soda lime glass; and the thermoplastic polymer material comprises a layer of polyvinyl butyral.

21. The method of any one of claims 12-20, further comprising: stacking the laminated sheet of glass and one or more further laminated sheets of glass (one by one) to form a stack of laminated sheets of glass before the heating, each of the one or more further laminated sheets of configured in substantially the same manner as the laminated sheet of glass, wherein the stack of laminated sheets of glass is heated to soften the thermoplastic polymer material in each of the laminated sheet of glass and the one or more further laminated sheets of glass, wherein the force is utilized on the stack of laminated sheets of glass to reduce the bow of each of the laminated sheet of glass and the one or more further laminated sheets of glass while the thermoplastic polymer material is softened, andwherein the stack of laminated sheets of glass is cooled so as to harden the thermoplastic polymer material and reduce the bow of each of the laminated sheet of glass and the one or more further laminated sheets of glass.

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