Glazing comprising a floating Anti-static layer

Abstract

The invention relates to laminated glazing comprising a first outer glass sheet (2) having a thickness of between 0.5 and 5 mm and at least one structural glass sheet (3, 3') bonded in pairs by an intermediate adhesive layer (4, 6), the laminated glazing being attached to a mounting structure by being clamped by a retainer (1) bolted thereto and electrically integral with the mass thereof, the free surface of the first glass sheet (2) supporting a floating anti-static layer (8) having an electrical conductivity of less than 10 MOhm per square, and located at most 10 mm from the retainer (1), or more than 10 mm from the retainer (1), and the main surface of the first glass sheet (2) internal to the structure of the laminated glazing supporting an electrode (9) electrically integral with the mass of the mounting structure. The invention further relates to the use of the laminated glazing as aircraft glazing.

Description

[0001] Description

[0002] Title of the invention: Glazing with floating antistatic layer

[0003] Aeronautical glazing is generally made of electrically insulating materials (glass, PMMA, PC, etc.) which tend to become electrically charged in certain environments through triboelectric effects. These environments include, for example, dust clouds from volcanic eruptions, snow, and ice crystals. Typical currents that may be encountered are a few hundred uA / m 2 of glazing. For such currents, flows in the thickness and on the surface of the glazing can be neglected.

[0004] This creates a surface potential for the glazing that is different from that of the aircraft structure, which is generally equipped with passive dissipators.

[0005] In addition, aeronautical glazing is generally equipped with an anti-frost system covering all or part of the laminated surface of the glass (organic or mineral) exposed to load phenomena on its other side (external glass sheet, or external glass).

[0006] Under loading conditions this results in:

[0007] - an intense electric field in the thickness of the external glass (between its heating face and its charged face) which can induce a dielectric breakdown in its thickness and its ruin;

[0008] -significant electrical energy stored in the capacitor formed by the thickness of the external glass (dielectric) and the two electrodes that are its two surfaces. This energy can power tree-like surface discharges between the structure of the aircraft on the periphery of the glazing and the surface of the glazing. These discharges cause:

[0009] - electromagnetic radiation that can disrupt the aircraft's electronics;

[0010] - overvoltages or overcurrents, particularly on the temperature sensor circuits opposite the heating layer and used to regulate the temperature of the glazing to prevent icing;

[0011] -dazzling of pilots by the luminous radiation of the discharges.

[0012] Establishing a surface discharge requires a plasma with sufficient energy at the discharge tip. In practice, for a 3 mm thick glass and at an atmospheric pressure of 1 bar, a surface potential of at least 25 kV is required for surface discharges to be established.

[0013] For all these reasons, it is sometimes necessary to provide an electrostatic discharge system which can: i - be made up of a surface treatment of the glass aimed at giving it dissipative (electrical) properties and connected to the ground of the aircraft;

[0014] - equip the external surface of the glazing with metal tips connected to the aircraft ground allowing an early corona discharge. This second solution is not applicable to mineral glass because in practice it is necessary to pierce the external glass to run a wire to its surface. It is therefore more often used on pierceable plastic glazing. The first solution can be applied to mineral glasses by applying a durable coating of the indium tin oxide type (in English "Indium Tin Oxide" - ITO-) or diamond-like carbon (in English "Carbon Like Diamond" - DLC) or sub-stoichiometric oxide. On organic glasses conductive layers can also be applied but they are generally sensitive to scratching. For all these solutions, the electrical charges are drained to the aircraft ground via electrical wires.

[0015] Managing the routing of electrical wires to the aircraft ground leads to complexities related to issues of space requirement, and / or visibility and / or interface and / or durability of the wire-dissipative layer connection. In particular, since the dissipative layers are on the surface of the glazing, they are subject to eroding environments. An electrical connection on this surface leads to an excess thickness increasing exposure to erosion and requiring a non-flush protection strategy (aerodynamic disturbance, aerodynamic noise, erosion and associated maintenance). Finally, the attachment of lightning to these drains connected to the aircraft ground in its internal part can lead to:

[0016] - structural degradation of the glazing;

[0017] - electromagnetic radiation inside the aircraft structure;

[0018] -heating and projections of molten metal inside the aircraft which could cause fires.

[0019] The invention was made by asking whether the above problems could not be eradicated by leaving the antistatic layer floating, i.e. not electrically connected to the ground of the mounting structure (in particular aircraft fuselage). The system must then be designed to promote discharges that do not degrade the performance of the aircraft. These questions could be answered favorably by the invention which, consequently, relates to a laminated glazing comprising a first glass sheet and at least one structural glass sheet bonded two by two by an interlayer adhesive layer, the main free surface of the first glass sheet being intended to be in contact with the external atmosphere, the first glass sheet being set back relative to said at least one structural glass sheet, and having a thickness of between 0.5 and 5 mm,the edges of the first glass sheet and the first interlayer adhesive layer, and the free part of the main surface of the structural glass sheet, extending beyond the first glass sheet, forming a cavity for receiving a retainer for fixing by pinching the laminated glazing to a mounting structure of the mass of which the retainer is electrically integral, said free surface of the first glass sheet supporting an antistatic layer not electrically integral with the mass of the mounting structure, and of electrical conductivity less than 10 MOhm per square, characterized in that at least one point of the antistatic layer is located at most 10 mm from the retainer, or the antistatic layer is entirely located more than 10 mm from the retainer and the main surface of the first glass sheet internal to the structure of the laminated glazing supports an electrode electrically integral with the mass of the mounting structure.

[0020] When two flat electrodes are opposite each other, from a threshold electric field (breakdown field), a discharge can start and almost instantly generate an arc. The discharge phase corresponds to the establishment of a sufficient electric field for a first ionization (ionizing radiation for example) to generate an avalanche of ionizations. The electrons are in fact accelerated by the effects of the electric field and can then, by electron bombardment of the gases, generate other ionizations. Other mechanisms are involved (excitation of molecular species, UV radiation, photo-ionization, electronic emission under ion and electron impact, electronic attachment, etc.).

[0021] The arc results from the creation of a conductive path in the air by heating the air by the passage of current. In plane / tip or tip / tip configurations, the electric field is not homogeneous and is more intense near the tips. Only a volume near the tips is then capable of causing ionization avalanches. The discharge remains localized near the tips. This is called corona discharge or partial discharge. Despite its partial nature, this discharge is capable of flowing a current of the order of mA / cm for linear geometries, i.e. a high current compared to the charging currents on aeronautical glazing, of the order of a few hundred uA / m 2 under heavy load conditions.

[0022] The electric field generated by charged elements can generate atmospheric plasmas. Ionized species (ions and electrons) are then transported by electric fields and in particular charges can be transported towards insulating surfaces such as glass. In the event of partial discharge initiation, the electric fields are modified by space charges in the air (separation of differently charged species and different mobility of species) and on insulating surfaces. Since the mobility of surface charges is much lower than that of charges in the atmospheric phase, it is the latter which have the greatest influence on the potentials. Thus, for low-intensity discharges, the potentials of the insulators will be established in such a way that no net current is collected.

[0023] For practical reasons, it is extremely complicated to ensure continuity between the antistatic layer and the retainer. There is therefore a dielectric space on the surface of the glazing between the edge of the antistatic layer and the metal retainer. In a charging environment, different potentials are established between the retainer, the surface of the antistatic layer and the insulating dielectrics. This results in intense electric fields, particularly due to the peak effect at the edge of the metal structure and at the edge of the (very thin) antistatic layer. This results in the initiation of partial discharges generating a plasma charging the surface of the dielectrics.

[0024] In equilibrium conditions, the surface of the dielectrics is at intermediate potentials between the metal structure and the antistatic layer. The peak effects are then screened by the space charges on the dielectrics. This results in extinction of the partial discharges. It is then possible to reach in the air gap between the retainer and the antistatic layer potential lines that are relatively parallel to each other and perpendicular to the surface of the glazing, characteristics of plane / plane discharges and therefore the discharge criteria are governed by Paschen's law. These discharges have an immediate transition into an arc. Since the arc currents are very high, the charges of the antistatic layer cannot feed the arc by conduction in the latter but only by displacement of the arc head on the surface of the antistatic layer. This is the surface discharge mechanism already described.To avoid these discharges, it is necessary to ensure that the potential of the glass is lower than the potential necessary to establish surface discharges (typically 25 kV for a 3 mm glass). The breakdown fields described by Paschen's law are 30 kV / cm at atmospheric pressure (worst case). To allow partial discharges, the layer edge must be located less than 8 mm from the retainer at at least one point.

[0025] Thus, according to the first alternative of the invention, the floating antistatic layer with electrical conductivity less than 10 MOhm per square positioned on a glass of 0.5 to 5 mm is located at least at one point less than 10 mm from an element electrically integral with the aircraft mass.

[0026] According to the second alternative of the invention, an electric field singularity is generated in the vicinity of the edge of the floating antistatic layer by means of an electrode integral with the plane mass present in the laminate, ideally on the internal surface of the external glass. In this second alternative or configuration, the electric field is more influenced by the potential of the laminate electrode than by the retainer.

[0027] Here again, the initiation of discharges causes a deposit of charges on the surface of the glass in such a way that the electric field on the surface of the glass is parallel to it in the active zone of the discharge. In this case, the influence of the ground electrode makes it possible to create a peak effect at the edge of the layer.

[0028] If the edge of the antistatic layer is sufficiently far from the edge of the retainer, a corona discharge can then be generated which does not attach to the glazing retainer, thus avoiding any degradation of the latter.

[0029] Such a configuration is known as a dielectric barrier discharge and can typically initiate partial discharges for 3 mm of glass from a potential difference between the antistatic layer and the ground electrode of 6 kV for a 3 mm thick glass. It is therefore a milder discharge mode than that of the first alternative of the invention.

[0030] According to the invention, a glass sheet designates both a sheet of mineral glass of the soda-lime, aluminosilicate, borosilicate, float type, possibly thermally toughened or chemically reinforced, and a sheet of transparent polymer material such as poly(methyl methacrylate) (PMMA), polycarbonate (PC), poly(ethylene terephthalate) (PET), polyurethane (PU)... The first glass sheet is a relatively thin surfacing sheet, unlike the structural sheet(s), designating sheets capable of guaranteeing the mechanical properties required for laminated glazing, in particular in the case where the latter must delimit a pressurized volume such as an airplane. When the structural block comprises only one glass sheet, it is considered to be structural provided that its elastic modulus is at least equal to 1500 MPa for example.The structural glass sheet(s) is (are) for example made of mineral glass with a thickness of between 1.6 and 10 mm, or of PMMA type polymer material with a thickness of between 3 and 30, preferably at most 20 mm.

[0031] An interlayer adhesive layer is made of a thermoplastic polymer, mainly polyvinyl butyral (PVB), thermoplastic polyurethane (TPU), ethylene-vinyl acetate copolymer (EVA), casting resin, ionomer resin. The thickness of the first interlayer adhesive layer bonding the first glass sheet to the first structural sheet is between 3 and 10, preferably 4 and 8 mm, while the thickness of the following interlayer adhesive layer(s) bonding structural sheets two by two is between 0.5 and 4 mm, preferably at most 2 mm. Preferably, the antistatic layer is made of doped oxide such as indium tin oxide (ITO) or aluminum zinc oxide (AZO), non-stoichiometric oxide such as SnCh, or diamond-like carbon (DLC), with a thickness of between 5 nm and 1 μm, preferably between 10 and 50 nm.The antistatic layer can be deposited on the glass by PVD (Physical Vapor Deposition) means, for example by magnetic field-assisted cathode sputtering - magnetron under reduced pressure, or by liquid means, for example sol-gel.

[0032] Preferably, the antistatic layer has an electrical conductivity of at least 100 Ohm per square, preferably 10 kOhm per square, and at most 100 kOhm per square.

[0033] Preferably, the electrode is closer to the retainer than the antistatic layer, by a distance preferably at least equal to the thickness of the first glass sheet, the edge of the electrode distal to the retainer is closer to the latter than the proximal edge of the antistatic layer by a distance at most equal to the thickness of the first glass sheet, at most by a distance at most equal to the characteristic dimensions of the main surfaces of the first glass sheet, and the length of the electrode in the direction normal to the retainer is at least equal to the thickness of the first glass sheet.

[0034] Preferably, the proximal edge of the antistatic layer relative to the retainer is straight and parallel to the latter, or has tip effects to promote the initiation of electrical discharges.

[0035] In the latter case, the proximal edge of the antistatic layer relative to the retainer comprises tips preferably in the form of triangles, rectangles longer than they are wide, rectangles with rounded corners or rectangles ending in triangles, the sides of the rectangles or triangles being rectilinear or curved so as to form concave or convex edges, and the tips being entirely opposite the electrode if it exists. The tips can be obtained by selective ablation of the antistatic layer, for example by means of a laser, by a mechanical or chemical method. They can be obtained by masking in the deposition step.

[0036] Preferably, the electrode constitutes the anti-icing heating layer or is an additional electrode such as indium tin oxide (ITO) or equivalent. If the laminated electrode is the heating layer itself, it will then be ensured that in the non-heating phases, the latter remains at the potential of the mounting structure.

[0037] The invention also relates to the use of a laminated glazing described above as aircraft cockpit glazing, in particular windshield, in particular for medium and long-haul commercial aircraft, business aircraft, tourist aircraft. The invention will be better understood in the light of the following description of the appended drawings in which

[0038] [Fig. 1] is a schematic sectional view of a glazing unit of the state of the art; [Fig. 2] is a schematic sectional view of a glazing unit according to the first alternative of the invention;

[0039] [Fig. 3] is a schematic sectional view of a glazing according to the second alternative of the invention;

[0040] [Fig. 4] is a partial schematic representation of a glazing according to the second alternative of the invention;

[0041] [Fig. 5] and [Fig. 6] are two schematic front views of the exterior of glazing in accordance with the invention.

[0042] With reference to Figure 1, a commercial aircraft windshield representative of the state of the art consists of a thin outer sheet 2 of glass bonded to a relatively thick structural glass sheet 3 by means of a relatively thick layer 4 of TPU. The glass sheet 3 constitutes the structural block of the laminate with the relatively thick structural glass sheet 3', to which it is bonded by a fairly thin layer 6 of PVB. The laminated glazing rests on an inner retainer 1', which may be the aircraft structure, with the interposition of a shim 7. The glazing is fixed to the mounting structure by the retainer 1, an outer retainer consisting of a glass press which, by being bolted to the aircraft structure, exerts pressure on the edge of the structural block 3, 6, 3' by means of the silicone seal 5.

[0043] An electrical connection is established between the antistatic layer 8 and the aircraft ground (not shown). This connection can be obtained by bonding using a conductive glue 11, a first conductive connection element 10 and a routing wire 10' to a connection to the aircraft ground. Depending on the case, 10 and 10' can be a single cable or preferably a thin element of the metal foil type for 10 and a cable 10' for example brazed to each other. Such an assembly requires protection 12 against the eroding environment and moisture penetration. The internal face of the laminated structure of the first glass sheet 2 or outer glass sheet supports an anti-icing heating layer 9 made of ITO, connected to the ground of the aircraft structure via electrical sources. This configuration has the drawbacks described previously.

[0044] Figure 2 describes the first alternative of the invention. Here, the antistatic layer 8 is floating, or in other words, is not electrically connected to the ground of the aircraft structure. The antistatic layer 8 is at most 10 mm away from the retainer 1 (or ice press). A corona discharge 20 at the edge of the antistatic layer 8, a corona discharge 21 at the edge of the retainer 1, and an electric arc 22 between the antistatic layer 8 and the retainer 1 are shown. The transition from the corona discharges 20 and 21 to the electric arc 22 may exceptionally occur but in an unstable manner and without causing a surface discharge. Figure 3 describes the second alternative of the invention, according to which the antistatic layer

[0045] 8 is located entirely more than 10 mm from the retainer 1 and the heating layer or electrode

[0046] 9 is electrically secured to the mass of the mounting structure, so that the electrical discharges are preferentially carried out at the edge of the antistatic layer thanks to the amplification of the electric field generated by the proximity of the electrode 9. The electrical charges are then put into the air and can be all or partly recollected by the aircraft but without a discharge phenomenon. The corona discharge 21 and the electric arc 22 of Figure 2 no longer occur, unlike the corona discharge 20 which is maintained.

[0047] Referring to Figure 4, the relative positions of the antistatic layer 8, the laminated electrode 9 and the retainer 1 or glass press are shown, according to the second alternative of the invention. These relative positions can be defined by the fact that u is positive, preferably greater than a thickness e of external glass 2; v between -e and any positive value less than the characteristic size of the external glass 2 (length L and width 1 of its main surfaces); u+v > e; and D > 10mm.

[0048] The edge of the antistatic layer 8 may be generally straight or textured so as to form points or fingers oriented towards the retainer 1 (first alternative of the invention), and / or entirely opposite the laminated electrode (second alternative of the invention). In the Error! Reference source not found, and Error! Reference source not found, the retainer 1 and two configurations of the antistatic layer 8 having a pointed edge are shown, configurations representative of both the first alternative of the invention (D <

[0049] 10 mm), and the second (D > 10 mm). Typically, e' will be chosen to be less than or equal to the thickness of the outer glass 2, d greater than or equal to the thickness of the outer glass 2 and L greater than the thickness of the outer glass 2. The discharge zone consists of a layer of the same nature as the antistatic layer 8 and whose edges are formed by masking during deposition, ablation after deposition for example by laser, or additional deposition of conductive elements by bonding or screen printing for example. The proposed solution is to be compared to a glazing not provided with an antistatic solution on the one hand and to a glazing equipped with an antistatic layer discharged by a drain on the other hand. Compared to solutions without an antistatic layer, the solution of the invention makes it possible to eliminate dazzling and radiant discharges (electromagnetic, visual and sound disturbances).

[0050] The implementation of a conductive drain between the external surface of a glazing and the internal structure of the aircraft has the following limitations: complexity of implementing a reliable electrical connection between a non-metallic layer and a metallic drain (bonding, differential expansions, sensitivity to humidity, etc.); protrusion (aerodynamic impact, including noise); risk of breakage of the glazing or internal fire in the aircraft in the event of lightning attachment to the drain.

[0051] These limitations are resolved by the present invention.

Claims

Claims 1. Assembly or module comprising a laminated glazing unit comprising a first glass sheet (2) and at least one structural glass sheet (3, 3') bonded two by two by an interlayer adhesive layer (4, 6), the main free surface of the first glass sheet (2) being intended to be in contact with the external atmosphere, the first glass sheet (2) being set back relative to said at least one structural glass sheet (3, 3'), and having a thickness of between 0.5 and 5 mm, the assembly or module comprising a retainer (1) for fixing by pinching the laminated glazing unit to a mounting structure of the mass of which the retainer (1) is capable of being electrically integral in the mounting position of the laminated glazing unit, the edges of the first glass sheet (2) and of the first interlayer adhesive layer (4), and the free part of the main surface of the structural glass sheet (3), overhanging the first glass sheet (2),forming a cavity for receiving the retainer (1), said free surface of the first glass sheet (2) supporting an antistatic layer (8) with an electrical conductivity of less than 10 MOhm per square, characterized in that in the mounting position of the laminated glazing, the antistatic layer (8) is configured to be non-electrically integral with the retainer (1) on the one hand, with the mass of the mounting structure on the other hand, at least one point of the antistatic layer (8) is located at a non-zero distance of 10 mm at most from the retainer (1), or the antistatic layer (8) is entirely located more than 10 mm from the retainer (1) and the main surface of the first glass sheet (2) internal to the structure of the laminated glazing supports an electrode (9) configured to be electrically integral with the mass of the mounting structure., 2. Assembly or module according to claim 1, characterized in that the antistatic layer (8) is made of doped oxide such as indium tin oxide (ITO) or aluminum zinc oxide (AZO), of non-stoichiometric oxide such as SnCh, or of diamond-like carbon (DLC), with a thickness of between 5 nm and 1 μm, preferably between 10 and 50 nm.

3. Assembly or module according to one of the preceding claims, characterized in that the antistatic layer (8) has an electrical conductivity at least equal to 100 Ohm per square, preferably 10 kOhm per square, and at most equal to 100 kOhm per square.

4. Assembly or module according to one of the preceding claims, characterized in that in the mounting position of the laminated glazing, the electrode (9) is closer to the retainer (1) than the antistatic layer (8), by a distance preferably at least equal to the thickness of the first glass sheet (2), the edge of the electrode (9) distal to the retainer (1) is closer to the latter (1) than the proximal edge of the antistatic layer (8) by a distance at most equal to the thickness of the first glass sheet (2), at a distance at most equal to the characteristic dimensions of the main surfaces of the first glass sheet (2), and the length of the electrode (9) in the direction normal to the retainer (1) is at least equal to the thickness of the first glass sheet (2). Assembly or module according to one of the preceding claims, characterized in that in the mounting position of the laminated glazing, the proximal edge of the antistatic layer (8) relative to the retainer (1) is straight and parallel to the latter (1), or has tip effects to promote the initiation of electric discharges.Assembly or module according to one of the preceding claims, characterized in that in the mounting position of the laminated glazing, the proximal edge of the antistatic layer (8) relative to the retainer (1) comprises points in the form of triangles, rectangles longer than they are wide, rectangles with rounded corners or rectangles ending in triangles, the sides of the rectangles or triangles being rectilinear or curved so as to form concave or convex edges, and the points being entirely opposite the electrode (9) if it exists. Assembly or module according to one of the preceding claims, characterized in that the electrode (9) constitutes the anti-frost heating layer or is an additional electrode such as in indium tin oxide (ITO) or equivalent.Use of an assembly or module according to one of the preceding claims as aircraft cockpit glazing, in particular windshield, in particular for medium and long-haul commercial aircraft, business aircraft, tourist aircraft.

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