Tempered vacuum insulating glazing with compression resistant discrete spacers

Abstract

The present invention relates to a vacuum insulating glazing unit (10) extending along a plane, P, defined by a longitudinal axis, X, and a vertical axis, Z, and having a core region and comprising: i a first glass pane and a second glass pane, wherein the first and / or second glass pane is / are tempered; ii. a set of discrete spacers (4) positioned between the first and second glass panes, maintaining a distance between the first and the second glass panes, each discrete pillar encompassed within the core region, supports an effective area, Aeff, defining an effective pitch, λeff, being the square root of the effective area (Formula I); iii. a hermetically bonding seal sealing the distance between the first and second glass panes over a perimeter thereof; iv. an internal volume, defined by the first and second glass panes and the set of discrete spacers and closed by the hermetically bonding seal and wherein there is a vacuum of absolute pressure of less than 0.1 mbar. The effective pitch, expressed in mm, is comprised between : (Formul II) wherein µ is the average discrete spacer resistance (N); and SD is the standard deviation of the average discrete spacer resistance (N).

Description

TEMPERED VACUUM INSULATING GLAZING WITH COMPRESSION RESISTANT DISCRETE SPACERS1. FIELD OF THE INVENTION

[0001] The present invention relates to tempered vacuum insulating glazing that comprise discrete spacers that demonstrate proper resistance to compression and therefore provide superior resistance to external stresses while maintaining superior thermal insulating performance.2. BACKGROUND OF THE INVENTION

[0002] Current building market trend is to increase natural light and therefore the glazing surface, while minimizing the energy consumption of the building by using glazing having high insulating performances. Vacuum insulating glazing (VIG) are recommended because of their high-performance thermal insulation. A vacuum insulating glazing is typically composed of at least two glass panes separated by an internal space in which a vacuum has been generated. In general, in order to achieve a high-performance thermal insulation (Thermal transmittance, U, being U<1.2 W / m2K) the absolute pressure inside the glazing unit is typically 0.1mbar or less and generally at least one of the two glass panes is covered with a low-emissivity layer. To obtain such a pressure inside the glazing unit, a hermetically bonding seal is placed on the periphery of the two glass panes and the vacuum is generated inside the glazing unit by virtue of a pump. To prevent the glazing unit from caving in under atmospheric pressure (due to the pressure difference between the interior and exterior of the glazing unit), discrete spacers, are placed between the two glass panes.

[0003] Discrete spacers play a critical role in maintaining the physical integrity of the VIG and must be designed so that the VIG resist to different external stresses. Major external stresses to be considered are the thermal stress induced by a temperature difference between exterior and interior environments, the atmospheric pressure induced stress and the stress caused by wind. The number and the distribution of the discrete spacers within the VIG must be carefully balanced: a higher number of discrete spacers provides more mechanical resistance of the VIG. However, such higher number of discrete spacers decreases the thermal insulation performance since they are responsible for heat conduction and therefore have a negative impact on the overall thermal insulation performance of the vacuum insulating glazing.

[0004] Typically for annealed glass, the limiting factor to design the distribution of pillars - also referred as discrete spacers, is the mechanical resistance of the glass panes since the number of discrete pillars is generally relatively high. WO2019219592 addresses the technical problem of improving the resistance to induced thermal stress in vacuum-insulated glazing units wherein glasspanes are subjected to temperature difference between exterior and interior environments and the resistance of atmospheric pressure induced stress at the pillar locations. This publication teaches to design a VIG with glass panes of different thicknesses, of a specified minimal length, of a specified minimal width, and of a specified thickness for the thinner glass pane (Z2), wherein the interval between the discrete spacers, X, has been carefully calculated in relation to the thickness of the thinner glass pane.

[0005] However, none of the art addresses the technical problem of the number, distribution and nature of the discrete pillars that must configured to maximize thermal insulation performance of VIG, while providing excellent mechanical resistance. Indeed, none of the art addresses the compression variability of the discrete spacers themselves, in particular for vacuum insulating glazing wherein at least one of the glass pane is tempered.3. SUMMARY OF THE INVENTION

[0006] Other aspects and advantages of the embodiments will become apparent from the following detailed description taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the described embodiments.

[0007] The present invention relates to a vacuum insulating glazing unit (VIG) extending along a plane, P, defined by a longitudinal axis, X, and a vertical axis, Z; and having a core region. The VIG comprises:i. a first glass pane, GP1, and a second glass pane, GP2, wherein the first and / or second glass pane is / are tempered;ii. a set of discrete spacers positioned between the first and second glass panes, maintaining a distance between the first and the second glass panes, each discrete spacer encompassed within the core region supports an effective area, Aeff, defining an effective pitch, λeff, being the square root of the effective area (λeff = √Aeff);ill. a hermetically bonding seal sealing the distance between the first and second glass panes over a perimeter thereof;iv. an internal volume, V, defined by the first and second glass panes and the set of discrete spacers and closed by the hermetically bonding seal and wherein there is a vacuum of absolute pressure of less than 0.1 mbar.The effective pitch, expressed in mm, is comprised between:√(μ − 2SD) / (0.2188) ≤ λeff ≤ √(μ − 2SD) / (0.1337)wherein μ is the average discrete spacer resistance (N); and SD is the standard deviation of the average discrete spacer resistance (N).

[0008] Preferably, the effective pitch, expressed in mm, is is comprised between:√(μ − 2SD) / (0.2006) ≤ λeff ≤ √(μ − 2SD) / (0.1337);preferably between: √(μ − 2SD) / (0.1823) ≤ λeff ≤ √(μ − 2SD) / (0.1337), more preferably between: √(μ − 2SD) / (0.1580) ≤ λeff ≤ √(μ − 2SD) / (0.1337),wherein μ is the average discrete spacer resistance (N); and SD is the standard deviation of the average discrete spacer resistance (N).

[0009] In another embodiment, the present invention relates to a VIG extending along a plane, P, defined by a longitudinal axis, X, and a vertical axis, Z, and having a core region. The VIG comprises: i. a first glass pane, GP1, and a second glass pane, GP2, wherein the first and / or second glass pane is / are tempered;ii. a set of discrete spacers positioned between the first and second glass panes, maintaining a distance between the first and the second glass panes, each discrete pillar encompassed within the core region supports an effective area, Aeff, defining an effective pitch, λeff, being the square root of the effective area (λeff = √Aeff);iii. a hermetically bonding seal sealing the distance between the first and second glass panes over a perimeter thereof;iv. an internal volume, V, defined by the first and second glass panes and the set of discrete spacers and closed by the hermetically bonding seal and wherein there is a vacuum of absolute pressure of less than 0.1 mbar,When processed up to its incorporation into the vacuum insulating glazing; the discrete spacer meets the following compression requirements in that its average discrete spacer resistance, p (expressed in N) and its standard deviation of the discrete spacer resistance, SD (expressed in N) are comprised between:0.1337 λeff2≤ (μ - 2SD) ≤ 0.2188 λeff2wherein λeff is the effective pitch.

[0010] Preferably, the discrete spacer when processed up to its incorporation into the vacuum insulating glazing; meets the following compression requirements in that its average discrete spacer resistance, p (expressed in N) and its standard deviation of the discrete spacer resistance, SD (expressed in N) are comprised between:0.1337 λeff2≤ (μ - 2SD) ≤ 0.2006 λeff2,preferably between: 0.1337 λeff2≤ (μ - 2SD) ≤ 0.1823 λeff2,more preferably between: 0.1337 λeff2≤ (μ - 2SD) ≤ 0.1580 λeff2,wherein λeff is the effective pitch.

[0011] In a preferred embodiment, the discrete spacers comprise a body and optionally a functional layer on at least a portion of the body, wherein a diameter of the discrete spacers is equal to or less than 600 microns, and a compressive strength of the discrete spacers material is equal to or greater than 400 MPa. Preferably, the discrete spacers are made of material selected from the group consisting of quartz glass, ceramic, sintered ceramic, ceramic body with alpha alumina, zirconia, metals, resins and mixtures thereof.

[0012] More preferably the body of the discrete spacer is made of a resin material, preferably a polyimide resin material. In another preferred embodiment, the body of the discrete spacers comprise a material selected from the group consisting a sintered ceramic, ceramic body with alpha alumina, or zirconia and wherein the functional layer comprises a compliant layer comprising a thermally stable polymer, nanoparticles, a ferromagnetic layer, an electrically conductive, statically dissipative layer and / or an adhesive that preferably comprise a sacrificial material. Yet, in another preferred embodiment, the body of the discrete pillars has a 6-, 8-, or 12- sided shape with at least one tapered sidewall, a round shape with a tapered sidewall or a body with a tapered sidewall with a draft angle between 95° and 100°.

[0013] It is preferred that the discrete spacer have a contact surface to the glass pane equal to or lower than 0.5mm2, preferably equal to or lower than 0.3mm2, more preferably equal to or lower than 0.2mm2and even more preferably equal to or lower than 0.1mm2.

[0014] The first glass pane, GP1, and the second glass pane, GP2, can be tempered. The thickness of the glass panes are typically comprised between 3mm and 10mm, preferably between 4mm and 8mm, more preferably between 4mm and 6mm. It is preferred that the first glass pane may have a coefficient of thermal expansion, CTE1, and the second glass pane has a coefficient of thermal expansion, CTE2, wherein the absolute difference between CTE1 and CTE2 may be at most 0.40 10-6 / °C ( | CTE1-CTE21 <0.4010-6 / °C); preferably is at most 0.3010-6 / °C ( | CTE1-CTE21 <0.3010-6 / °C), more preferably at most 0.20 10-6 / °C ( | CTE1-CTE21 <0.20 10-6 / °C) and even more preferably wherein the coefficient of thermal expansion, CTE1, of the first glass pane is equal to the coefficient of thermal expansion, CTE2, of the second glass pane.4. BRIEF DESCRIPTION OF THE DRAWINGSFIG.1(a) shows a top view of a vacuum insulating glazing according to one embodiment of the present invention wherein the glazing has a rectangular shape.FIG.1(b) shows a top view of a vacuum insulating glazing according to another embodiment of the present invention wherein the glazing has a half circle shape.FIG.2(a) and FIG.2(b) illustrate a Voronoi tessellation of an array of discrete spacers arranged at a regular pitch according to a centered-hexagonal distribution or according to a centered-rectangular distribution.5. DETAILED DESCRIPTION OF THE INVENTION

[0015] The objective of the present invention is to provide a vacuum insulating glazing having the highest thermal performance while maintaining its mechanical integrity. Vacuum insulating glazing is herein referred to as " VIG". " Discrete spacer" or "pillar" will be used interchangeably herein.

[0016] An object of the present invention is to provide a tempered vacuum insulating glazing wherein the number, distribution, material and processing of the discrete pillars are carefully selected so that the glazing demonstrates not only improved mechanical resistance but as well has excellent thermal insulating performance.

[0017] By mechanical resistance, it is commonly understood that the VIG of the present invention must demonstrate proper resistance to the thermal induced stress, the wind induced stress as well as to atmospheric pressure induced stress, that are faced by the glass panes:(1) Thermal induced stresses occur as soon as there is a temperature difference between the temperature, T1, of the external surface of the first glass pane and the temperature, T2, of the external surface of the second glass pane, when the first and second glass panes are not free to move relative to one another, e.g., because of the peripheral bonding seal or because of a frame clamping a perimeter of the VIG. The thermal stresses increase with increasing differences between the temperatures, T1 and T2. Thermal stresses can be induced on the glass panes for example, when a VIG is exposed to severe temperature differences between interior and exterior spaces, typically when the VIG separates an interior from an exterior environment. In most stringent conditions, the difference between the interior and exterior temperatures can reach up to 40°C and more. When exposed to different temperatures, the two glass panes expand differently. Since they are not free to move relative to one another because, on the one hand, of the peripheral bonding seal and, on the other hand, of the frame clamping the VIG, the different thermal expansions of the two glass panes of the VIG bend the panes and therefore create stresses.(2) Wind induced stress refers to the amount of pressure caused by wind that the glazing must be able to resist. When calculating wind loads for architectural glazing projects there are many factors that need to be considered, including the buildings height, shape, relationship to surrounding buildings and the terrain as well as the local wind speeds and gust durations.(3) The atmospheric pressure induced stress is the result of the atmospheric pressure applied on the external surfaces of the glass panes of the VIG. The internal surfaces of the glass panes are exposed to a vacuum whilst the external surfaces of the glass panes are exposed to atmospheric pressure bending the sheets towards one another. The presence of the discrete spacers separating the two glass panes, however, prevents the two glass panes from contacting, but induces permanent tensile stresses on the external surfaces of the glass panes above each discrete spacer. It is known by the skilled person that for small pillars, the tensile stress induced by the pillars at the external surfaces of the glass panes is independent of the size of its external circumference.

[0018] It is well recognized in that art that the number, distribution and nature of the pillars play a critical part in the mechanical resistance and thermal insulation performance of the VIG. The number and distribution of pillars are commonly addressed as "pitch". Typically for annealed glasses, the limiting factor to design the pitch is the mechanical resistance of the glass panes since discrete pillars are generally relatively large. To increase thermal performance, one option is to decrease the size of the pillars but it negatively impacts the pillars mechanical resistance. Another option would be to temper the glass pane(s), allowing to increase the pitch but increased pitch increases the load that needs to be supported by each pillar. In all instances, the mechanical resistance of the pillars themselves becomes the critical design factor.

[0019] The present invention is based on the careful study and analysis of the different factors that will impact the resistance of each pillar to compression. It has been found that not only the stresses on the glass panes should be considered but as well the specific load on each pillars. Furthermore, it has been found that the individual pillar resistance, R, must exceed the expected resistance to be provided by each individual pillar.

[0020] (1) The individual pillar resistance, R, is typically assessed as R ≥ 0.1013 * λeff2wherein 0.1013 refers to the atmospheric induced stress and λeff is the pitch.

[0021] (2) The present invention is based on the surprising understanding that that nominal pillar resistance is also impacted by the resistance of its neighbouring pillars. The potential weakness of defective neighbouring pillars must also be considered. By defective pillar, it is understood by a damaged pillar or a missing pillar. Defective pillars induce an increase of stress to be supported by their neighbouring pillars, of about 20%.

[0022] (3) When designing a VIG, it has been further surprisingly found that overload caused by the non-planarity of the tempered glass pane must also be further considered. The non-planarity of tempered glass pane - also referred to as the flatness effect caused by the roll distortion, is the periodic wave imparted to glass during heat treatment. These roll waves are always present at some level in heat treated glass due to the glass being transported horizontally on rollers in the tempering furnace. Depending on the glass thickness, roll wave distortion (also referred to as flatness induced stress) may induce an increase of stress supported by some of the pillars comprised between about 10% for very low roll distortion of the glass pane, about 50% for medium roll distortion, to about 80% for high roll distortion of the glass pane.

[0023] Therefore, the present invention is based on the technical understanding that the individual pillar resistance, R, must exceed the expected resistance to be provided by each individual pillar to encompass not only the atmospheric induced stress but as well the overload induced by defective pillars and by roll distortion of tempered glass panes.

[0024] (4) In addition, the compression profile of the pillars must be carefully considered. Pillar resistance to compression depends on its material and on its production method. For most pillar materials, it has been further found that not only the average pillar resistance (p) expressed in N must be considered but as well its variability versus the average discrete spacer resistance, as defined by the standard deviation of the average discrete spacer resistance, SD, expressed in N.

[0025] Therefore, it has been found that the objectives of the present invention of mechanical resistance combined with superior thermal insulation performance, are met when not only the external induced stress on the glass panes are considered, but as well when the additional stresses on the discrete pillars induced by defective pillars, atmospheric pressure and roller wave distortion in addition to the compression profile of the discrete pillars are taken into account.

[0026] The vacuum insulating glazing unit extends along a plane, P, defined by a longitudinal axis, X, and a vertical axis, Z. It has a width, W, measured along the longitudinal axis, X, and a length, L, measured along the vertical axis, Z. The VIG has a surface along the plane, P, limited by borders. The first glass pane has a thickness Zl, and a second glass pane has a thickness, Z2, wherein the thicknesses are measured in the direction normal to the plane, P.

[0027] Typically, pillars are arranged on the glass pane surface in a regular manner forming a regular array. In some configurations, the pillars may be distributed according to one more different regular arrays. In particular, it can happen that the distribution of the pillars is denser, i.e. the number of pillarsis higher in the regions wherein the external stresses are more important, such as along the edges and in the corners and the distribution is more dispersed in the regions wherein the external stresses are less important, such as in the center of the glazing. As commonly understood "regular" means arranged according to the same and uniform distribution pattern. To avoid the side effect and / or to avoid the effect of a higher number of pillars along the edges and / or in the corner, a VIG core region is herein defined.

[0028] To any shape corresponds a characteristic dimension, CD, being the diameter of its circumscribed circle. Hence, a border region of the VIG can be defined on the plane P, to comprise all points that are located at a distance of less than 5% of the length of the characteristic dimension, CD, from the VIG borders. The core region is then defined as the surface of the VIG without the border region.

[0029] FIG. la illustrates a VIG (10) of a rectangular shape, that has been circumscribed in its circle (20) that defines its characteristic dimension, CD being the longest diagonal of the rectangular VIG. A border region (1) has been defined to comprise all points that are located at a distance of less than 5 of the length of the characteristic dimension, CD, from the VIG border (3). The core region (2) is then defined as the surface of the VIG without the border region (1). The VIG comprises a regular square array of discrete spacers (4).

[0030] FIG. lb illustrates a VIG (10) of a half circle shape, that has been circumscribed in its circle (20) that defines its characteristic dimension, CD, being the diameter the VIG. A border region (1) has been defined to comprise all points that are located at a distance of less than 5% of the length of the characteristic dimension, CD, from the VIG border (3). The core region (2) is then defined as the surface of the VIG without the border region (1). The VIG comprises a regular square array of discrete spacers (4).

[0031] The VIG of the present invention comprises a set of discrete pillars positioned between the first and second glass panes, maintaining a distance between them. Each discrete spacer has a supporting effect on the glass panes over a given area of influence, bonded by areas of influence of the neighboring discrete spacers. Such situation can be described using Voronoi cells forming a Voronoi tessellation. In mathematics, a Voronoi tessellation or diagram is a partitioning of a plane into regions based on distance to points in a specific subset of the plane. That set of points is formed by the n discrete spacers distributed over the planar area. For each discrete spacer there is a corresponding region consisting of all points closer to that discrete spacer than to any other. These regions are called " Voronoi cells", or simply "cells" having a cell area (Ai), which defines the area of influence of eachdiscrete spacer. A Voronoi tessellation formed by n cells is characterized by a cell area distribution. The cell areas (Ai) of a Voronoi tessellation increases with decreasing number, n, of discrete spacers per unit area. For example, a first VIG comprising a number pl of discrete spacers smaller than a number p2 of discrete spacers of a second VIG is characterized by a cell area distribution having a larger mean cell area than a second VIG or of a second portion of the VIG.

[0032] FIG.2(a) illustrates the Voronoi tessellation of an array of discrete spacers arranged at a regular pitch according to a centered-hexagonal distribution. The Voronoi cells are all hexagonal of same dimensions with the corresponding discrete spacer centered therein. FIG2(b) illustrates the Voronoi tessellation of an array of discrete spacers arranged at a regular pitch according to a centered-rectangular distribution. The Voronoi cells are all rectangular of same dimensions with the corresponding discrete spacer centered therein.

[0033] For the purpose of the present invention, only the cell areas (Ai) of the pillars comprised within the core region (2) will be considered and their mean surface area will be calculated to provide the effective area (Aeff).

[0034] Strictly speaking, the "pitch, λ," is only used for characterizing square arrays of discrete spacers and is understood to mean the shortest distance separating a given discrete spacer from any of its neighbors. However, to apply to any regular arrangement of discrete spacers, the definition of the "pitch, X," has been extended to the square root of the Effective Area, Aeff, and has been named " Effective pitch, Xeff" wherein λeff = √Aeff. This alternative definition respects the original definition applicable to square arrays and allows an at least partial characterization of any arrangement of discrete spacers.

[0035] For square based regular arrays, the effective area, Aeff, corresponds to λ2wherein λ is the pitch wherein pitch is indeed understood to mean the shortest distance separating a given discrete spacer from any of its neighbors. For rectangular based regular arrays, the effective area, Aeff, corresponds to λ1 x λ2 wherein λ1 is understood to mean the shortest distance separating a given discrete spacer from any of its neighbors and λ2 is the understood to mean the shortest distance separating a given discrete spacer from any of its neighbors in a direction perpendicular to direction of the shortest distance λ1.

[0036] For square based regular arrays, the atmospheric pressure induced stress also referred to as tensile stress, can be calculated by the following formula: σp= 0.11× λeff2 / t2[MPa] wherein Aeff [m] is the pitch between the spacers and t [m] is the glass panes thickness.

[0037] In the case of annealed VIG, the atmospheric pressure induced stress, crp must be typically lower than lOMPa, preferably lower than 5MPa, to avoid glass breaking. Therefore, for a VIG with glass panes of specific thicknesses, the atmospheric induced stress define a limitation on the pitch to maintain mechanical resistance of the VIG. In the case of tempered VIG, the mechanical resistance of the glass pane is highly superior, about 80MPa, and therefore, the limit on the pitch is substantially released. In those instances, it has been found that there is an additional constrain that needs to be taken into account: even if glass pane could mechanically resist to the external stresses, the discrete pillars themselves could crush. Indeed, it has been surprisingly found that there is a critical relation between the pitch and the compression resistance profile of the pillars that must be fulfilled to achieve the objectives of the present invention.

[0038] The present invention relates to a tempered vacuum insulating glazing wherein the effective pitch (Xeff) meets the following inequations that takes into account the stresses supported by the glass panes as well as all loads supported by each discrete spacer. The effective pitch, expressed in mm, is is comprised between:(p- 2SD) / (0.2188) < Xeff < ^(p - 2SD) / (0.1337) wherein p is the average discrete spacer resistance (N); and SD is the standard deviation of the average discrete spacer resistance (N).

[0039] The numerical value takes into account the atmospheric induced stress, the defective pillar induced stress and the flatness effect of the tempered glass pane(s). It has been found that a VIG designed with a set of discrete spacers having an effective pitch, Xeff, meeting the above inequations, will provide the proper mechanical resistance with tempered glass pane(s) of any flatness profile.

[0040] In a preferred embodiment, the effective pitch, expressed in mm, is is comprised between:√(μ − 2SD) / (0.2006) ≤ λeff ≤ √(μ − 2SD) / (0.1337)Preferably, is comprised between:√(μ − 2SD) / (0.1823) ≤ λeff ≤ √(μ − 2SD) / (0.1337)And more preferably, is comprised between:√(μ − 2SD) / (0.1580) ≤ λeff ≤ √(μ − 2SD) / (0.1337) wherein μ is the average discrete spacer resistance (N); and SD is the standard deviation of the average discrete spacer resistance (N).

[0041] In another embodiment of the present invention, the above relationship can be reformulated to calculate to the requirements of the discrete spacers expected to obtain a VIG of a specified thermal performance for glass panes of any tempering quality. The expected thermal insulation performance will be set by a specified effective pitch, Xeff. It has been found that he discrete spacer when processed up to its incorporation into the vacuum insulating glazing, should meet the following compression requirements in that its average discrete spacer resistance, p (expressed in N) and its standard deviation of the discrete spacer resistance, SD (expressed in N) are comprised between:0.1337 λeff2≤ (μ - 2SD) ≤ 0.2188 λeff2wherein Xeff is the effective pitch.

[0042] In a preferred embodiment, the compression requirement is comprised between:0.1337 λeff2≤ (μ - 2SD) ≤ 0.2006 λeff2,preferably between: 0. 1337 λeff2≤ (μ - 2SD) ≤ 0.1823 λeff2,more preferably between: 0. 1337 λeff2≤ (μ - 2SD) ≤ 0.1580 λeff2,wherein Xeff is the effective pitch.

[0043] By discrete spacer compression properties, it is herein understood the average discrete pillar resistance, μ, expressed in (N) measured as per testing method described below and the standard deviation of the discrete spacer resistance, SD, expressed in (N); for a discrete spacer of a certain dimension, certain shape and of a certain material and that has been processed up to its direct incorporation into the VIG production process.

[0044] The compression resistance of the pillar is measured by the following method:(1) Samples preparation: a glass plate of dimensions 100mmx100mmx4mm is prepared. A pillar is prepared according to the pillar making process used within the VIG making process. If pillars are submitted to any preparation step(s) before their placement, such steps(s) should be performed before the measurement takes place.(2) Test procedure: A pillar is placed at the centre on the first glass plate, as shown in Figure 3.The glass plate - with the added pillar, is then fixed in the test machine. A compression force is applied on the pillar, using a press fixture in the perpendicular direction to the glass plate, as shown in the figure below. The force is applied at a speed of 10mm / minute until breakage. The maximum force corresponding to the breakage of the pillar is then recorded. As commonly understood, the breakage point is determined by the sudden decrease of 10% of the maximum applied compression force.The compression resistance of 100 discrete spacers are measured and recorded. The average discrete spacer resistance, p, and the standard deviation, SD, of the discrete spacer resistance are calculated as per classical statistical method.SPACERS

[0045] The discrete spacers comprised in the VIG of the present invention can have different shapes, such as cylindrical, spherical, filiform, hourglass shape, C-shaped, cruciform, prismatic shape. Discrete spacers have a contact surface to the glass pane, defined by its external circumference, generally comprised between 2mm2and 0.2mm2. In the present invention, it is preferred to use small discrete spacers, i.e. have a contact surface to the glass pane equal to or lower than 0.5mm2, preferably equal to or lower than 0.3mm2, more preferably equal to or lower than 0.2mm2and even more preferably equal to or lower than 0.1mm2

[0046] The discrete spacers are typically made of a material having a strength endurable against pressure applied from the surfaces of the glass panes, capable of withstanding high-temperature process such as burning and baking, and hardly emitting gas after the glass pane is manufactured. Such a material is preferably a hard metal material such as quartz glass, ceramic or metal. In particular, the metal material is such as iron, tungsten, nickel, chrome, titanium, molybdenum, carbon steel, chrome steel, nickel steel, stainless steel, nickel-chromium steel, manganese steel, chromium-manganese steel, chromiummolybdenum steel, silicon steel, nichrome, duralumin or the like. Another such material can be a ceramic material such as corundum, alumina, mullite, magnesia, yttria, aluminum nitride, silicon nitride or the like. Other suitable materials are resins, preferably made of polyimide resin.

[0047] Other suitable discrete spacers are described in patent publication WO2015 / 038391 published on March 19; 2015 by 3M innovative Properties Company on page 3, line 5 to page 12, line 17 which is herein incorporated by reference. Such discrete spacers comprise a body and optionally a functional layeron at least a portion of the body, wherein a diameter of the discrete spacers is equal to or less than 600 microns, and a compressive strength of the discrete spacers material is equal to or greater than 400 MPa and hence an average discrete spacer resistance, p, equal to or greater than 1000N. Preferably, the body of the discrete spacer comprises a sintered ceramic, ceramic body with alpha alumina, or zirconia. Preferably, the functional layer comprises a compliant layer comprising a thermally stable polymer, nanoparticles, a ferromagnetic layer, an electrically conductive, statically dissipative layer and / or an adhesive that preferably comprise a sacrificial material. The discrete spacers can have different shapes such as a body with a 6-, 8-, or 12- sided shape with at least one tapered sidewall or a round shape with a tapered sidewall or a body with a tapered sidewall with a draft angle between 95° and 100°. The discrete spacers may be monolithic or composite. Composite discrete spacers may comprise a high compressive strength sintered ceramic core and one or more functional layers. Alternately, composite discrete spacers may comprise a thermally stable organic, inorganic, or hybrid polymeric binder and an inorganic nanoparticle filler.

[0048] A known technique to produce the discrete pillars, is achieved by subjecting a thin plate to a punching process. For example, EP0963961 uses a spacer formed in a cylindrical shape and has a diameter of 0.30 to 1.00 mm and a height of 0.1 to 0.5 mm. The method of producing the spacer, comprising preparing a thin plate (0.1 to 0.5 mm in thickness) of an aluminum alloy as the raw material. Then, by machining this thin sheet by means of e.g. punching, the cylindrical spacer having the predetermined diameter may be formed. A preferred technique for the processing of the pillars to be used for the VIG of the present invention is the laser cutting described in patent application EP3816128, filed under number 19825477.3 on May 16, 2019. That method includes: an irradiation step including setting, over a holder, a sheet for use to form pillars and irradiating the sheet with a laser beam to punch out the plurality of pillars; a holding step including having the plurality of pillars, which have been punched out of the sheet, held by the holder; and a mounting step including picking up some or all of the plurality of pillars from the holder and mounting the pillars onto the substrate. The discrete spacers obtained by such methods have significantly reduced burr. The pillar deliver apparatus is described in

[0024] to

[0034] and in reference with Figures 1 to 7 and the pillar delivery performance is described in

[0035] to

[0051] of EP3816128, all of which is incorporated herein by reference.GLASS COMPOSITION

[0049] In the present invention, at least one glass pane and preferably both glass panes of the VIG is / are tempered. By tempered glass, it is meant herein a heat strengthened glass or a thermally toughened safety glass.

[0050] Heat strengthened glass is heat treated using a method of controlled heating and cooling which places the outer glass surfaces under compression and the inner glass surface under tension. This heat treatment method delivers a glass with a bending strength greater than annealed glass but less than thermally toughened safety glass. Thermally toughened safety glass is heat treated using a method of controlled heating and cooling which puts the outer glass surface under compression and the inner glass surface under tension. Such stresses cause the glass, when impacted, to break into small granular particles instead of splintering into jagged shards. The granular particles are less likely to injure occupants or damage objects.

[0051] The VIG glass panes, can be chosen among float clear, extra-clear or colored glass. Typically, the glass panes are soda-lime-silica glass, aluminosilicate glass or borosilicate glass; preferably soda-lime-silica glass. Textured, structured, printed glass are suitable. The glass panes can optionally be edgeground for safety.

[0052] In an embodiment of the present invention, the first glass pane may have a coefficient of thermal expansion, CTE1, and the second glass pane has a coefficient of thermal expansion, CTE2, whereby the absolute difference between CTE1 and CTE2 may be at most 0.40 10'7°C ( | CTE1-CTE21 <0.40 10’7°C); preferably is at most 0.30 10’7°C ( | CTE1-CTE21 <0.30 10-6 / °C), more preferably at most 0.20 10'7°C ( | CTE1-CTE21 <0.20 10'7°C). Ideally, the first and second glass panes have the same coefficient of thermal expansion. This is preferred to improve the thermal performance and mechanical integrity. The term "coefficient of thermal expansion" (CTE) is a measure of how the size of an object changes with a change in temperature. Specifically, it measures the fractional change in volume of the glass pane per degree change in temperature at a constant pressure.

[0053] As known to persons skilled in the art, glass is an elastic material generally characterized by its Young's modulus, E, and Poisson 's ratio, p. The young's modulus is a measure of the stiffness whereby larger values indicate glasses that will hardly deform under applied stress. Typical values of the Young's modulus for soda-lime-silica, aluminosilicate or borosilicate glass compositions are comprised between 60 and 120 GPa (60 GPa < E < 120 GPa). In particular, soda-lime glass compositions present a Young's modulus value generally in the range from 69 to 72 Gpa (60 GPa < E < 72 GPa). The Poisson's ratio measures the Poisson effect, being a phenomenon whereby glass tend to expand in directions perpendicular to the direction of compression. Typical values of the Poisson's ratio for soda-lime-silica, aluminosilicate or borosilicate glass compositions are comprised between 0.18 and 0.30 (0.18 < p <0.30). In particular, soda-lime glass compositions present Poisson's ratio values generally in the range from 0.18 to 0.23 (0.18 < p <0.23).HERMETICALLY BONDING SEAL

[0054] The internal volume of the VIG is closed with a hermetically bonding seal placed on the periphery of the glass panes around said internal space. The hermetically bonding seal is impermeable to air or any other gas present in the atmosphere. Various hermetically bonding seal technologies exist. A first type of seal (the most widespread) is a seal based on a solder glass for which the melting point is lower than that of the glass panes of the glazing unit. Typically lower than 500°C, preferably lower than 450°C, more preferably lower than 400°C. Examples are low melting point glass frits such as bismuth based glass frits, lead based glass frits, vanadium based glass frits and mixtures thereof. A second type of seal comprises a metal seal, for example a metal strip of a small thickness (<500 pm) soldered to the periphery of the glazing unit by means of a tie underlayer covered at least partially with a layer of a solderable material such as a soft tin-alloy solder.INTERNAL VOLUME

[0055] A vacuum of absolute pressure less than 0.1 mbar, preferably less than O. Olmbar is created, within the internal volume, V, defined by the first and second glass panes and the set of discrete spacers and closed by the hermetically bonding seal. A getter can be used to maintain for the duration a given vacuum level in a vacuum-insulating glazing unit. Generally, such a getter consists of alloys of zirconium, vanadium, iron, cobalt, aluminum, etc., and is deposited in the form of a thin layer (a few microns in thickness) or in the form of a tablet placed between the glass panes.GLAZING

[0056] The VIG extends along a plane, P, defined by a longitudinal axis, X, and a vertical axis, Z. It has a width, W, measured along the longitudinal axis, X, and a length, L, measured along the vertical axis, Z. The first glass pane has a thickness Zl, and a second glass pane has a thickness, Z2, wherein the thicknesses are measured in the direction normal to the plane, P.

[0057] Typically the thickness of the glass panes are comprised between 3mm and 10mm, preferably between 4mm and 8mm, more preferably between 4mm and 6mm. The thickness of the glass panes of the VIG of the present invention can be the same or different. In the embodiment of the present invention, it might be indeed advantageous to design the VIG so the glass panes are of different thickness such that a thickness ratio, Z1 / Z2, of the thickness of the first glass pane, Zl, to the thickness of the second glass pane, Z2, is equal to or greater than 1.10 (Zl / Z2 > 1.10). Preferably, the thickness ratio, Z1 / Z2, is equal to or greater than 1.20 (Zl / Z2>1.20), preferably is equal to or greater than 1.30 (Zl / Z2>1.30), more preferably is equal to or greater than 1.55 (Zl / Z2>1.55), even more preferablycomprised between 1.60 and 6.00 (1.60 < Zl / Z2 < 6.00), ideally between 2.00 and 4.00 (2.00 < Z1 / Z2 < 4.00).

[0058] The design of the VIG of the present invention is of particular interest in designing glazing of large dimensions. By large dimensions, it is herein understood that the length of the VIG, L, is typically equal to or greater than 800 mm, (L > 800 mm), preferably equal to or greater than 1200 mm, (L > 1200 mm), more preferably equal to or greater than 1600 mm, (L > 1600 mm). The width of the VIG, W, is typically equal to or greater than 500 mm, (W > 500 mm), preferably equal to or greater than 800 mm, (W > 800 mm), more preferably equal to or greater than 1000 mm, (W > 1000 mm).

[0059] It is contemplated within the invention that the VIG comprises an additional glass pane(s) separated from the second glass pane by plurality of discrete spacers sandwiched between the additional glass pane and second glass panes so as to maintain an additional internal volume. Other multiple glazing comprises two, three or more singled glass sheets or laminated panes that are separated by a peripheral spacer extending along the edges of the glazing over a perimeter thereof, and maintaining a distance there between. It is also contemplated that the VIG of the present invention can replace one or more of glass pane(s) of such conventional multiple glazing.10 VIG1 Border region2 Core region3 VIG border4 Discrete spacer20 Circumscribed circleCD Characteristic DimensionAeff Effective Area

[0060] The person skilled in the art realizes that the present invention by no means is limited to the embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims. It is further noted that the invention relates to all possible combinations of features, and preferred features, described herein and recited in the claims. Examples are included for illustrating purposes only.EXAMPLESA VIG comprising two tempered glass panes and a 100% regular square array of polyimides resins discrete spacers with different Effective pitch, λEff, are used here below.

[0061] In example 1, the VIG has a relatively low effective pitch, λeff, of 20mm that is comprised between 20 and 25 (Table 1, example 1). Therefore, such pitch provides the required mechanical resistance to the VIG whatever the flatness of the tempered glass panes but is not very effective in terms of thermal insulation performance.

[0062] In order to increase the thermal insulation performance, the VIG of comparative example 2 has been designed with an effective pitch, λeff, of 30mm. However such larger pitch does not provide the required mechanical resistance since the effective pitch is above the maximal value of 25mm (Tables 1 and 2).

[0063] Comparative examples 3 illustrates a VIG having an intermediate effective pitch, λeff, of 29mm to provide better thermal insulation performance. The effective pitch of the VIG of comparative example 3 being outside of the required range of 22mm and 28mm does not provide the required mechanical resistance whatever the flatness of the tempered glass panes.

[0064] The VIG of example 4 has the same characteristics than comparative example 3 with the effective pitch λeff of 29mm but the discrete spacers have a lower standard deviation, SD, originating from an improved making process. The effective pitch of the VIG of example 4 must be comprised between 23mm and 30mm to provide the required mechanical resistance whatever the flatness of the tempered glass panes. The lower standard deviation of the average discrete spacer resistance of the discrete pillars of the VIG of example 4 versus comparative example 3 allows to design the VIG with a higher pitch range of 23mm-30mm versus 22mm-28mm. Hence the discrete spacer design of the VIG of example 4 provides the required mechanical resistance, whatever the flatness of the tempered glass panes. Higher effective pitch range provides better thermal insulation performance.Example 1 Example 2 Example 3 Example 4 Aeff (mm2) 400 900 841 841 λeff (mm) 20 30 29 29 Average discrete spacer116.7 116.7 140 140 resistance, p (N)Standard deviation of average16.9 16.9 16.9 10 discrete spacer resistance, SD (N)Lower limit7(p - 2SD) / (0.2188) 20 20 22 23 Upper limit to to to to 7(p - 2SD) / (0.1337) 25 25 28 30Valid Not Valid Not Valid Valid

Claims

CLAIMS1. A vacuum insulating glazing unit (10) extending along a plane, P, defined by a longitudinal axis, X, and a vertical axis, Z, and having a core region and comprising:i. a first glass pane and a second glass pane, wherein the first and / or second glass pane is / are tempered;ii. a set of discrete spacers (4) positioned between the first and second glass panes, maintaining a distance between the first and the second glass panes, each discrete spacer encompassed within a core region, supports an effective area, Aeff, defining an effective pitch, λeff, being the square root of the effective area (λeff = √Aeff); ill. a hermetically bonding seal sealing the distance between the first and second glass panes over a perimeter thereof;iv. an internal volume, defined by the first and second glass panes and the set of discrete spacers and closed by the hermetically bonding seal and wherein there is a vacuum of absolute pressure of less than 0.1 mbar,characterized in that the effective pitch, expressed in mm, is comprised between:√(μ − 2SD) / (0.2188) ≤ λeff ≤ √(μ − 2SD) / (0.1337)wherein p is the average discrete spacer resistance (N); and SD is the standard deviation of the average discrete spacer resistance (N).

2. A vacuum insulating glazing unit according to claim 1 wherein the effective pitch, expressed in mm, is is comprised between:(p - 2SD) / (0.2006) < Aeff < (p - 2SD) / (0.1337); preferably between ^ / (p — 2SD) / (0.1823) < Aeff < ^ / (p — 2SD) / (0.1337), more preferably between(p - 2SD) / (0.1580) < Aeff < ^(p - 2SD) / (0.1337), wherein p is the average discrete spacer resistance (N); and SD is the standard deviation of the average discrete spacer resistance (N).

3. A vacuum insulating glazing unit (10) extending along a plane, P, defined by a longitudinal axis, X, and a vertical axis, Z, and having a core region and comprising:i. a first glass pane and a second glass pane, wherein the first and / or second glass pane is / are tempered;ii. a set of discrete spacers (4) positioned between the first and second glass panes, maintaining a distance between the first and the second glass panes, each discrete pillarencompassed within a core region, supports an effective area, Aeff, defining an effective pitch, λeff, being the square root of the effective area (λeff = √Aeff);iii. a hermetically bonding seal sealing the distance between the first and second glass panes over a perimeter thereof;iv. an internal volume, defined by the first and second glass panes and the set of discrete spacers and closed by the hermetically bonding seal and wherein there is a vacuum of absolute pressure of less than 0.1 mbar,characterized in that the discrete spacer when processed up to its incorporation into the vacuum insulating glazing; meets the following compression requirements in that its average discrete spacer resistance, p (expressed in N) and its standard deviation of the discrete spacer resistance, SD (expressed in N) are comprised between:0.1337 Aeff2< (p - 2SD) < 0.2188 Aeff2wherein Aeff is the effective pitch.

4. A vacuum insulating glazing unit according to claim 3 wherein the discrete spacer when processed up to its incorporation into the vacuum insulating glazing; meets the following compression requirements in that its average discrete spacer resistance, p (expressed in N) and its standard deviation of the discrete spacer resistance, SD (expressed in N) are comprised between:

0. 1337 Aeff2< (p - 2SD) < 0.2006 Aeff2, preferably between:

0. 1337 Aeff2< (p - 2SD) < 0.1823 Aeff2, more preferably between:

0. 1337 Aeff2< (p - 2SD) < 0.1580 Aeff2, andwherein Aeff is the effective pitch.

5. A vacuum insulating glazing unit according to any one of the preceding claims wherein the first glass pane and the second glass pane, are tempered.

6. A vacuum insulating glazing unit according to any one of the preceding claims wherein the discrete spacers comprise a body and optionally a functional layer on at least a portion of the body, wherein a diameter of the discrete spacers is equal to or less than 600 microns, and a compressive strength of the discrete spacers material is equal to or greater than 400 MPa.

7. A vacuum insulating glazing unit according claim 6 wherein the discrete spacers are made of material selected from the group consisting of quartz glass, ceramic, sintered ceramic, ceramic body with alpha alumina, zirconia, metals, resins and mixtures thereof.

8. A vacuum insulating glazing unit according to claim 7 wherein the body of the discrete spacer is made of a resin material, preferably a polyimide resin material.

9. A vacuum insulating glazing unit according to claim 7 wherein the body of the discrete spacers comprise a material selected from the group consisting a sintered ceramic, ceramic body with alpha alumina, or zirconia and wherein the functional layer comprises a compliant layer comprising a thermally stable polymer, nanoparticles, a ferromagnetic layer, an electrically conductive, statically dissipative layer and / or an adhesive that preferably comprise a sacrificial material.

10. A vacuum insulating glazing unit according to claim 7 wherein the body of the discrete pillars has a 6-, 8-, or 12- sided shape with at least one tapered sidewall, a round shape with a tapered sidewall or a body with a tapered sidewall with a draft angle between 95° and 100°.

11. A vacuum insulating glazing unit according to any of the preceding claims wherein the discrete spacer have a contact surface to the glass pane equal to or lower than 0.5mm2, preferably equal to or lower than 0.3mm2, more preferably equal to or lower than 0.2mm2and even more preferably equal to or lower than 0.1mm2.

12. A vacuum insulating glazing unit according to any one of the preceding claims wherein the thickness of the glass panes are comprised between 3mm and 10mm, preferably between 4mm and 8mm, more preferably between 4mm and 6mm.

13. A vacuum insulating glazing unit according to any one of the preceding claims, wherein the first glass pane may have a coefficient of thermal expansion, CTE1, and the second glass pane has a coefficient of thermal expansion, CTE2, wherein the absolute difference between CTE1 and CTE2 may be at most 0.40 10’7°C ( | CTE1-CTE21 <0.40 10’7°C); preferably is at most 0.30 10⁻⁶ / °C ( |CTE1-CTE2|≤0.30 10⁻⁶ / °C), more preferably at most 0.2010’7°C ( | CTE1-CTE21 <0.20 10'7°C) and even more preferably wherein the coefficient of thermal expansion, CTE1, of the first glass pane is equal to the coefficient of thermal expansion, CTE2, of the second glass pane.

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