Ballistic resistant insulated glazing units

Technical Field

[0001] The present invention relates to security insulated glazing units.

Background Art

[0002] The overall terrorist threat to the security of the population has increased over recent years and remains on a sharp upward trajectory. Therefore, there is an increasing demand for a safer environment. Taking this on board, the security glazing industry needs to respond to a demand for large building fagade security.

[0003] Safety glazing and projectile / ballistic resistant glazing (BRG) are classes of optically transparent window products designed to protect occupants of buildings, transport vehicles, etc., from penetration by projectiles such as, but not limited to, windblown objects, bullets, and the like.

[0004] In exemplary window products, the outside surface of the window pane, the face receiving the incoming projectile, is generally referred to as the attack face, and the innermost surface of the window pane closest to the occupants of the building, vehicle, etc., is referred to as the protective side.

[0005] BRG products are typically constructed from several layers of glass and/or plastics or polymers. Conventional glass materials used for ballistic laminates include soda lime glass and borosilicate glass which are typically manufactured using a float process.

[0006] Other conventional glass materials used for ballistic laminates include crystalline materials such as aluminum oxy-nitride (ALON), spinel, sapphire, and glass-ceramic materials (GC). Multiple glass and/or plastic layers are typically bonded together in a lamination process using polymeric or adhesive interlayer materials to form a BRG window pane. Conventional BRG window panes are very thick and heavy, and the overall thickness, number of glass, plastic, and/or interlayer sheets, and the specific weight (e.g. mass per unit area) of the construction can be varied to resist various threat levels. These threat levels are generally a function of the type of projectile, the mass of the projectile and its construction, and velocity obtained from the explosive charge in the respective cartridge as well as the impact of one or more projectiles (typically three projectiles) within a predetermined area. Exemplary international ballistic standards include the European Standard (EN) 1063: 1999 Security Glazing Ballistic Standard.

[0007] While dealing with projectile-resistant security glazing for building applications, the European standard to fulfil is EN 1063. The glazing is assumed to be resistant against a given projectile if the glazing does not have any "through" holes, from the front to the back. The procedure for certification requires the definition of an attack face. This is the face of the projectile resistant glazing, marked by the manufacturer and/or supplier, as designed to face the ballistic. The certified glazing are rated in two categories‘S’ and‘NS’ stand for‘Splinters’ and‘No Splinters’. If no glass splinters emerge on the protective side after the ballistic test explained in the standard, the ballistic class additionally receives the rating "NS". If glass splinters emerge on the protected side of the impact-resistant glass after the ballistic test explained in the standard, "S" is added to the test result.

[0008] Each conventional BRG construction has its advantages and disadvantages depending upon the respective constituent layers. For example, all glass constructions are generally durable (not susceptible to scratching or UV attack) and are clear with little visual distortion; however, all glass constructions are heavy and are generally the thickest constructions. Acrylic constructions are relatively light but are not durable or optically clear without distortion.

[0009] Glass clad polycarbonate structures are generally lighter than all glass but suffer from optical visual distortions, and the polycarbonate layer is easily scratched. Thus, the polycarbonate layer is usually treated with an anti- scratch surface coating if exposed on a surface of the respective laminate structure. Furthermore, an additional UV coating is applied to stop detrimental yellowing of the polycarbonate material occurring with prolonged exposure to UV rays. Such coatings generally increase the expense of polycarbonate -based BRG constructions. It should also be noted that conventional acrylic and polycarbonate layers are susceptible to chemical degradation, e.g., methanol, toluene, acetone, methylene chloride, and gasoline. Defects caused by such chemical degradation range from cracking to tacky surfaces and/or sheer layer destruction, each of which negatively affects optical transparency and threat protection performance of a respective window pane.

[0010] As a good alternative, chemically tempered (CT) glass can be employed within BRG for achieving lighter and thinner structure. Indeed, including such kind of reinforced glass within a projectile-resistant composition allows to render the laminate much more flexible and resistant against the bullet impact. As a consequence, less glass are required to fully stop the bullet.

[001 1] While dealing with an projectile-resistant insulated glazing unit (IGU), it is common use to use a certified projectile-resistant single glazing unit (SGU) and to put it as the protective face of the IGU. In those instances when a bullet resistant glass component is used as the non-attack face of an insulating glass unit then there is no need to test. The classification of the insulating glass unit shall be the same as the glass component used (EN 1279-5).

[0012] As an example, a laminated glazing“5: 15: 15: 15: 15:5” (where means a layer of interlayer and the number is the thickness of the glass layer - This example is a 6 glass layers with 5 interlayers) is BR6 NS certified according to the test made regarding cited norms. The double glazing 4:4/15/5: 15: 15: 15:15:5 (where means a layer of interlayer, 715/” a gap of 15mm maintained by the spacer and the number is the thickness of the glass layer) is naturally BR6 NS certified without any complementary test.

[0013] In this configuration, only the back pane participate to the BR performance of the IGU. [0014] While in full agreement with the existing standards, this approach doesn’t allow to achieve thin projectile resistant IGU.

Summary of invention

[0015] It is an object of the present invention to alleviate these problems, and to provide an insulated glazing unit which leads to a reduction of the weight and the thickness of the unit and to a cost reduction.

[0016] According to a first aspect of the invention, the invention relates to an improved insulated glazing unit, configured for resisting to a projectile (6) with an kinetic impact energy, E, comprised between 1750 J and 1850 J (1750 J < E < 1850 J), extending along a plane, P, defined by a longitudinal axis, x, and a vertical axis, y, comprising :

a. a front laminated pane, F, facing the projectile, having a total thickness, ZF, and comprising m glass sheets f, each having a sheet thickness, Zf, bonded by m-1 polymer interlayers, each having a polymer thickness, Zfi, wherein m is a positive integer greater than or equal to 2 (m>2),

b. a back laminated pane B, having a total thickness, ZB, comprising at least n glass sheets, each having a sheet thickness, Zb, bonded by n- 1 polymer interlayers, each having a polymer thickness, Zbi, wherein n is a positive integer greater than or equal to 2 and

c. a spacer, S, maintaining a distance, D, between the front laminated pane F and the back laminated pane, B;

[0017] The thicknesses are measured in the direction normal to the plane, P. The total thickness of the front laminated pane, ZF, equals the sum of the thicknesses of the m glass sheets and the m-1 polymer interlayers and the total thickness of the back laminated pane, ZB, equals the sum of the thicknesses of the n glass sheets and the n-1 polymer interlayers.

[0018] The invention relates also to a process to produce an insulated glazing unit according to a first aspect of the invention. [0019] The solution as defined in the first aspect of the present invention is based on both panes can participate to the projectile resistance performance of the IGU. In this context, the front and back panes of the IGU play two different role : [0020] Front laminated pane (facing to the projectile) is dedicated for highly slowing down the bullet and absorbing the major part of its kinetic impact energy.

[0021] It is usually made of a plurality of thick glass with a so-called interlayer cushion at the end to efficiently absorb the remaining bullet kinetic impact energy. For this part, using tempered glass is not necessary since only a consequent amount of glass is needed to stop the bullet. An interlayer cushion is a polymer interlayer with a thickness of at least 1.5 mm. In case of the use of a PVB interlayer, the standard thickness of one layer is 0.76 mm in some cases this thickness of 0.76 mm can be obtained by two thin layers of 0.38 mm. To obtain a thicker PVB interlayer, several interlayers can be layered to obtain the desired thickness.

[0022] The insulated glazing unit is assumed to be resistant against a projectile with a given kinetic impact energy if the glazing does not have any "through" holes, from the front to the back. An IGU able to resist against a projectile with a given kinetic impact energy, E, between 1750 J and 1850 J (1750 J < E < 1850 J), according to standard EN 1063, will be classified BR5.

[0023] At this stage, the bullet can be mainly stopped but a splitting behaviour of the protective face can occur. To stop the inertia of the first pane, a second block or pane must be employed, the back laminated pane and must exhibit at least one of the two following characteristics high rigidity or high stress at failure.

[0024] The first alternative will ensure that the second bloc will not admit a deformation which could lead to its breakage. The second alternative will allow the second bloc to admit a bigger deformation than the one allowed in the first alternative without breakage. This second alternative leads to the decrease of the laminated thickness and requires to work with tempered glass.

[0025] The solution as defined in the first aspect of the present invention that the total thickness of the back laminated assembly, ZB, is at most 1/3 of the sum of the total thickness of the front laminated pane, ZF, and the total thickness of the back laminated pane, ZB (ZB < 1/3 ^* (ZF + ZB)) and in that at least 2 glass sheets of the back laminated pane, ZB, are tempered.

[0026] In a preferred embodiment to minimize the weight of the laminated assembly, the total thickness of the back laminated assembly, ZB, is at most 1/4 of the sum of the total thickness of the front laminated pane, ZF, and the total thickness of the back laminated pane, ZB (ZB < 1/4 ^* (ZF + ZB)) and more preferably, the total thickness of the back laminated assembly, ZB, is at most 1/5 of the sum of the total thickness of the front laminated pane, ZF, and the total thickness of the back laminated pane, ZB (ZB < 1/5 ^* (ZF + ZB)). This allows to facilitate transport, handling, mounting,...

[0027] The thickness of a laminated pane is the sum of the thicknesses of the glass sheets added to the thicknesses of the interlayers. Glass sheet comprised in a laminated pane can have a different thickness such as polymer interlayers.

[0028] Glass sheets of the IGU of the present invention within laminated assemblies can be chosen among all flat glass technologies, among them: float clear, extra-clear or coloured glass. The term “glass” is herein understood to mean any type of glass or equivalent transparent material, such as a mineral glass. The mineral glasses used may be irrespectively one or more known types of glass such as soda-lime-silica, aluminosilicate or borosilicate, crystalline and polycrystalline glasses. The glass pane can be obtained by a floating process, a drawing process, a rolling process or any other process known to manufacture a glass pane starting from a molten glass composition. The glass sheets can optionally be edge-ground. Edge grinding renders sharp edges into smooth edges which are much safer for people who could come in contact with the insulating glazing unit, in particular with the edge of the glazing. Preferably and for reasons of lower production costs, the glass pane according to the invention is a pane of soda-lime-silica glass, aluminosilicate glass or borosilicate glass.

[0029] In some embodiments of the present invention, films such as low emissivity films, solar control films (a heat ray reflection films), anti-reflective films, anti- fog films, preferably a heat ray reflection film or a low emissivity film, can be provided on at least one of the inner sheet faces and/or outer sheet faces of the laminated panes.

[0030] Laminated panes within the IGU of the present invention may typically comprise from 2 to 10 glass sheets corresponding to m and n, positive integers, preferably from 2 to 7 glass sheets and at least corresponding layers of polymer interlayers (m-1 and n-1).

[0031] The polymer interlayer to be used in the present invention typically comprises a material selected from the group consisting ethylene vinyl acetate (EVA), polyisobutylene (PIB), polyvinyl butyral (PVB), polyurethane

(PU), polyvinyl chlorides (PVC), polyesters, copolyesters, polyacetals, cyclo olefin polymers (COP), ionomers and/or an ultraviolet activated adhesive, and others known in the art of manufacturing glass laminates. Blended materials using any compatible combinations of these materials can be suitable as well. In a preferred embodiment, the at least one polymer interlayer comprises a material selected from the group consisting of ethylene vinyl acetate, and/or polyvinyl butyral, more preferably polyvinyl butyral. The polymer interlayer is also designated as a“bonding interlayer” since the polymer interlayer and the glass pane form a bond that results in adhesion between the glass pane and the polymer interlayer.

[0032] In a preferred embodiment, the polymer interlayer to be used in the present invention is a transparent or translucent polymer interlayer. However, for decorative applications, the polymer interlayer may be coloured or patterned. [0033] Typical thicknesses (measured in the direction normal to the plane, P) for the at least one polymer interlayer are 0.3 mm to 3.5 mm, preferably 0.75 mm to 1.75 mm. Commercially available polymer interlayers are polyvinyl butyral (PVB) layers of 0.38 mm, 0.76 mm, 1.52 mm, 2.28 m and 3.04 mm. To achieve the desired thickness, one or more of those layers can be used.

[0034] To form the laminate assembly within the IGU of the present invention, polyvinyl butyral polymer interlayers are preferably used. Polyvinyl butyral (or PVB) is a resin known for applications that require strong binding, optical clarity, adhesion to many surfaces, toughness and flexibility. It is prepared from polyvinyl alcohol by reaction with butyraldehyde. Trade names for PVB-films include KB PVB, Saflex, GlasNovations, WINLITE, S-Lec, Trosifol and EVERLAM. The bonding process takes place under heat and pressure also designated as autoclave process which is well known in the art. When laminated under these conditions, the PVB interlayer becomes optically clear and binds the two panes of glass together. Once sealed together, the laminate behaves as a single unit and looks like normal glass. The polymer interlayer of PVB is tough and ductile, so brittle cracks will not pass from one side of the laminate to the other.

[0035] Another process known in the art and preferred for the present invention, is the autoclave free laminated glass production. This process reduces kinetic impact energy costs but has the drawback of limiting the types. Autoclave free oven makes preferentially EVA and dedicated PVB laminated glass. In such case, to achieve the desired thickness and security requirements, one or more of those autoclave free polymer interlayers can be used. The usual process for such autoclave free interlayers is the vacuum bag process

[0036] In one embodiment according to the invention, at least one of tempered glass sheets of the insulated glazing unit is chemically tempered to improve the bending stress of the tempered glass sheet.

[0037] In a preferred embodiment, the distance, D, is equal to or greater than 6mm (D>6 mm), preferably equal to or greater than 9mm (D > 9mm). In another preferred embodiment, the distance, D, is equal to or lower than 25 mm (D < 25 mm), preferably equal to or lower than 20 mm (D < 20 mm), more preferably equal to or lower than 15 mm (D < 15 mm). Hence, the distance D is typically comprised between 6 mm and 25 mm (6 mm < D < 25 mm), preferably between 9 mm and 20 mm (9 mm < D < 20 mm), more preferably between 9 mm and 15 mm (9 mm < D < 15 mm).

[0038] In another embodiment, the back laminated pane has an outer pane face coupled to a third glass pane along the periphery of the insulating glazing unit via a peripheral spacer bar, creating an insulating cavity sealed by a peripheral edge seal.

[0039] In a preferred embodiment, at least one glass sheet of the front laminated pane is tempered and preferably chemically tempered.

[0040] In a preferred embodiment, at least one of tempered glass sheets of back laminated pane is placed at the opposite face from the face facing the projectile and in a more preferred embodiment, at least one of tempered glass sheets of back laminated pane is placed at the opposite face from the face facing the projectile to maximize the total performance of the laminated assembly to maximize the total performance of the laminated assembly.

[0041] In a preferred embodiment to ensure the protection of the user in the opposite side of the laminated assembly from the projectile, all tempered sheets of back laminated pane are placed at the opposite face from the face facing the projectile.

[0042] The invention relates also to a process to manufacture an insulated glazing unit comprising a front laminated pane facing the projectile and comprising at least m glass sheets bonded by at least m-1 polymer interlayers, m is a positive integer greater or equal to 2, a back laminated pane comprising at least n glass sheets bonded by at least n-1 interlayers, n is a positive integer greater or equal to 2 and a spacer maintaining a distance, D, between the front laminated pane and the back laminated pane. [0043] The process comprises a step to assembly the front laminated pane and the back laminated pane with a spacer to maintain a distance D between laminated panes, and the thickness of the back laminated pane is at most 1/3 of the total thickness of the front laminated pane and preferably 1/4 of the total thickness of the front laminated pane and more preferably 1/5 of the total thickness of the front laminated pane, and at least 2 glass sheets of the back laminated pane are tempered.

[0044] It is noted that the invention relates to all possible combinations of features recited in the claims. [0045] The following description relates to an architectural window unit but it’s understood that the invention may be applicable to others fields like automotive.

Brief description of drawings

[0046] This and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing various exemplifying embodiments of the invention which are provided by way of illustration and not of limitation. The drawings are a schematic representation and not true to scale. The drawings do not restrict the invention in any way. More advantages will be explained with examples. [0047] FIG. 1 is a schematic view of a glazing panel according to an exemplifying embodiment of the present invention.

Description of embodiments

[0048] With reference to FIG. 1 , a first embodiment of the present invention is described. [0049] FIG. 1 shows an insulated glazing unit (10) configured to resist to a projectile

(6) with an kinetic impact energy, E, comprised between 1750 J and 1850 J (1750 J < E < 1850 J), extending along a plane, P, defined by a longitudinal axis, X, and a vertical axis, y, comprising : a. a front laminated pane, F, facing the projectile, having a total thickness, ZF, and comprising m glass sheets, f, each having a sheet thickness, Zf, bonded by m-1 polymer interlayers, fi, each having a polymer thickness, Zfi, wherein m is a positive integer greater than or equal to 2 (m>2)

b. a back laminated pane B, having a total thickness, ZB, comprising at least n glass sheets, each having a sheet thickness, Zb, bonded by n- 1 polymer interlayers, bi, each having a polymer thickness, Zbi, wherein n is a positive integer greater than or equal to 2 and c. a spacer, S, maintaining a distance, D, between the front laminated pane F and the back laminated pane, B wherein the thicknesses are measured in the direction normal to the plane, P, in the axis, z.

[0050] Wherein the total thickness of the front laminated pane, ZF, equals the sum of the thicknesses of the m glass sheets and the m-1 polymer interlayers, and wherein the total thickness of the back laminated pane, ZB, equals the sum of the thicknesses of the n glass sheets and the n-1 polymer interlayers.

[0051] In a particular embodiment of the fig. 1 according of the invention, the front glass pane comprises four glass sheets (f 1 , f2, f3, and f4) and three interlayers (fi1 , fi2, fi3). The thickness of each glass sheet is respectively Zf 1 , Zf2, Zf3 and Zf4. The thickness of each polymer interlayer is respectively Zfi1 , Zfi2 and Zfi3. The total thickness of the front laminated pane, ZF = Zf1 + Zfi1 + Zf2 + Zfi2 + Zf3 + Zfi3 + Zf4. The back laminated pane comprises three glass sheets (b1 , b2, b3) and two interlayers (bi 1 , bi2). The thickness of each glass sheet is respectively Zb1 , Zb2 and Zb3. The thickness of each polymer interlayer is respectively Zbi 1 and Zbi2. The total thickness of the front laminated pane, ZB = Zb1 + Zbi1 + Zb2 + Zbi2 + Zb3.

[0052] Each thickness of each glass sheet , Zf1 , Zf2, Zf3, Zf4, Zb1 , Zb2 and Zb3, can be different and each thickness of each polymer interlayer, Zfi 1 , Zfi2, Zfi3, Zbi 1 and Zbi2, can be different independently the number of glass sheet used (m or n). [0053] Surprisingly, to limit the weight of the structure by keeping same performances as a non-tempered laminated assembly according to norms, inventors shown that at least two glass sheets of the back laminated pane have to be tempered. The thickness of the back laminated assembly, ZB, can be reduced and limited to at most 1/3 of the sum of the thicknesses of the front and the back laminated panes (ZF + ZB).

[0054] In a preferred embodiment, glass sheet b1 or b2 is tempered and glass sheet b3 is tempered. Glass sheet b3 is the glass sheet of the back laminated assembly placed at the opposite face from the face (f1a) facing the projectile (6).

[0055] In a more preferred embodiment, at least glass sheets b2 and b3 are tempered meaning the furthest away from the projectile two glass sheets when the back laminated pane comprises three glass sheets understood that the back laminated pane is not limited in term of number of glass sheets Preferably, the back laminated pane comprises two to five glass sheets (2 < n < 5) and more preferably at most four glass sheets (n < 4)

[0056] In some embodiment, all glass sheets of the back laminated pane can be tempered.

[0057] In some embodiment, at least one glass sheet of the front laminated pane is tempered to limit the weight of the front laminated pane and preferably, the tempered glass is the closest glass sheet, f 1 , from the projectile.

[0058] The person skilled in the art realizes that the present invention by no means is limited to the preferred embodiments described above or to the examples described below. On the contrary, many modifications and variations are possible within the scope of the appended claims.

Example

[0059] Examples E1 and E2 illustrate different embodiments of IGU of the present invention, demonstrating the required resistance to projectile (BR5). Examples E3 illustrate a comparative embodiment of IGU. Configurations and thicknesses of examples are shown in Table 1.

[0060] Examples E1 and E2 and the comparative example E3 are classified BR5 NS according to standard EN 1063.

Table 1 : Examples - configurations and thicknesses

Example E1

[0061] The IGU of the example E1 comprises a front laminated pane (F) and a back laminated pane (B) maintained at a distance D = 9 mm. The front laminated pane of this specific embodiment comprises four (m = 4) glass sheets (f 1 , f2, f3 and f4) and three polymer interlayers (fi 1 , fi2 and fi3). The back laminated pane comprises two (n = 2) tempered glass sheets (b1 and b2) and one interlayer (bi1 ).

[0062] Glass sheets and polymer interlayers have different thicknesses (respectively Zfl , Zf2, Zf3, Zf4, Zfi1 , Zfi2, Zfi3, Zb1 , Zb2 and Zbi1 ) as shown in Table 1 at the corresponding line in the column E1. The total thickness of the front laminated pane (ZF) is the sum of thicknesses of glass sheets and polymer interlayers; ZF = Zf1 + Zf2 + Zf3 + Zf4 + Zfi1 + Zfi2 + Zfi3 = 4 + 8 + 8 + 4 + 0.76 + 0.76 + 2.28 = 27.8 mm. The total sum of the back laminated glass (ZB) is the sum of thicknesses of glass sheets and polymer interlayer; ZB = Zb1 + Zb2 + Zbi1 = 4 + 4 + 0.76 = 8.76 mm. The ratio of the back laminated pane is the thickness of the back laminated pane divided by the sum of the thicknesses of the front and the back laminated panes, ZB/(ZF

+ ZB) = 8.76/(27.8 + 8.76) = 0.24. Thus, ZB = 0.24 ^* (ZF + ZB).

[0063] The IGU of example 1 allows to reduce the total weight by keeping same properties such as BR5NS.

Example E2 [0064] Examples E2 is an IGU according to the invention in comparison with example E3 with same performances but much thicker and heavier than E2. Another advantage of the IGU according to the invention is to provide a thinner IGU. Thus, handling, transportation and manipulations are facilitated. Installers can mount assemblies according to the invention in an easier way to reduce risk of breakage, pain and falls.

[0065] The IGU of the example E2 comprises a front laminated pane (F) and a back laminated pane (B) maintained at a distance D = 15 mm. The front laminated pane of this specific embodiment comprises four (m=4) glass sheets (f 1 , f2, f3 and f4) and three polymer interlayers (f i 1 , f i2 and fi3). The back laminated pane comprises two (n = 2) tempered glass sheets (b1 and b2) and one interlayer (bi1 ).

[0066] Glass sheets and polymer interlayers have different thicknesses (respectively Zfl , Zf2, Zf3, Zf4, Zfi1 , Zfi2, Zfi3, Zb1 , Zb2 and Zbi1) as shown in Table 1 at the corresponding line in the column E2. The thickness of the front laminated pane is 32.56 mm and the back laminated pane is 8.76 mm.

The ratio of the thickness of the back laminated pane is 0.21 (ZB/(ZF + ZB) = 8.76/(27.8 + 8.76) = 0.24). Thus, ZB = 0.24 ^* (ZF + ZB). Example E3 - comparative example

[0067] In the case where the ratio and/or the back laminated pane does not have at least two tempered glass sheets, a IGU to obtain same performances (BR5 NS) as previous examples E1 and/or E2, an IGU has to be thicker. The comparative example E3 is an IGU without any tempered glass sheet.

[0068] The IGU of the example E3 comprises a front laminated pane (F) and a back laminated pane (B) maintained at a distance D = 15 mm. The front laminated pane of this specific embodiment comprises four (m=4) glass sheets (f 1 , f2, f3 and f4) and three polymer interlayers (f i 1 , f i2 and fi3). The back laminated pane comprises three (n = 3) glass sheets (b1 , b2 and b3) and two interlayers (bi 1 and bi2). None of glass sheets is tempered.

[0069] Glass sheets and polymer interlayers have different thicknesses (respectively Zf 1 , Zf2, Zf3, Zf4, Zfi1 , Zfi2, Zfi3, Zb1 , Zb2, Zb3n Zbi1 and Zbi2) as shown in Table 1 at the corresponding line in the column E3. The thickness of the front laminated pane is 32.56 mm and the back laminated pane is 17.52 mm. The ratio between the thickness of the back laminated pane and the thickness of the back laminated pane is 0.35 (ZB/(ZF + ZB) = 0.35). Thus, ZB = 0.35 ^* (ZF + ZB). Example 3 is heavier than the structure of the example E2 according to the invention for a BR5 NS performances. [0070] There are known solutions to improve the example E3 but all these solutions have an overcost and/or aesthetic problems.

[0071] For example, a layer of polycarbonate laminated with poly-urethane layer can be added to the assembly. However, polycarbonate suffers from several drawbacks such as bad aesthetic durability (yellowness), high cost, processing problem with glass assembly and the thermal expansion coefficient is so different from the one of the glass than delaminations can occur.

[0072] Another advantage of the IGU according to the invention is to provide a thinner IGU. Thus, handling, transportation and manipulations are facilitated. Installers can mount assemblies according to the invention in an easier way to reduce risk of breakage, pain and falls.

[0073] IGUs according to the present invention are thinner than other known IGU with same performances even if it exists an overcost for the tempering...