Field of the invention The present invention relates to a method for shielding glass surfaces of buildings from electromagnetic waves.

Furthermore, the invention relates to a glass panel for the building industry that carries out this method.

Background of the invention The problem is felt of shielding houses and offices from electromagnetic waves, whose negative effects on health and on well-being, notwithstanding not yet completely understood, are feared by people.

In particular, houses and offices are the places where people spend most of time, and then where the exposition is the largest.

New buildings have always thin walls, even if rugged enough, and are substantially permeable to electromagnetic waves.

In particular, roofs of buildings often support repeaters or other antennas that emit electromagnetic waves, whereby inhabitants are more exposed to this type of radiation. Near buildings there are sometimes high voltage lines, that create intense and variable electric and magnetic fields.

Furthermore, electronic instruments and apparatus are negatively affected by the presence of electromagnetic waves.

In a building, the points most permeable to electromagnetic waves are the glass surfaces.

It is furthermore in certain cases felt the problem of shielding from radio transmissions rooms where secret discussions occur and in which microphones could be

installed. Owing to the high permeability to radio frequencies of glass surfaces of buildings to electromagnetic waves, microphones even very small installed in a room could transmit conversations also hundreds meter away and allow to other people to listen to them.

For achieving the object of shielding buildings, it is furthermore relevant to have sufficiently transparent glass surfaces for allowing light to pass and to illuminate the rooms.

On the other hand, the need is felt of attenuating the sunlight that passes through the glass surfaces of buildings, for example by means of smoked glasses, sun blinds, shutters, etc. In particular, in houses and in the public places the attenuation of the sunlight is obtained with aesthetically valuable systems, which can be coloured.

It is well known from US 4613530 a multiple glass panel that comprises inside a transparent conductive film used as an anti radiation shield. The transparent film is covered by antioxidant layers that give at the same time stiffness. The combination of the film and of the protective layers is kept stretched by the frame of the panel. A portion of the film protrudes from the panel and is grounded, to provide the shielding.

This type of panel overcomes in part the above problems of shielding and of transparency. However, it does not provide an attenuation of the sunlight contemporaneous to partially or totally shielding electromagnetic waves.

EP 291591 describes also an electromagnetic shield for windows of buildings, and comprises a transparent film and a grounding by means of direct connection to the metal frame of the window and to metal structural elements of

the building. The transparent film is mounted directly on the glass with a protective antioxidant film put thereon.

However, the metal nets used in such cases are normally antiaesthetical and create an excessive attenuation of sunlight. Furthermore they are quickly oxidised and turn into a dark colour. Therefore, they are not suitable for cases where at the same time functions of shielding and esthetical functions are implemented, as required in the building industry.

It is also known from EP0902614 an electromagnetic- wave shielding and light transmitting plate comprising two transparent plates and a conductive mesh member arranged therebeween. The mesh is bonded between the base plates and has margins folded along the peripheral edge and secured with an adhesive tape. The shielding is used as a front filter for a Plasma Display Panel (PDP).

Summary of the invention It is an object of the present invention to provide a method for protecting glass surfaces of buildings capable of shielding rooms from electromagnetic waves, which is easy to carry out both on existing doors or windows and on doors or windows being built.

It is another object of the present invention to provide a method for shielding glass surfaces of buildings from electromagnetic waves that allows at the same time enough transparency to light coming from the outside and, at the same time, provides an attenuation of the sunlight without the need of treating the glass and of sun blinds.

It is a further object of the present invention to provide a glass panel for the building industry that allows good permeability to light from the outside and is at the same time impermeable to electromagnetic waves.

It is a particular object of the present invention to provide a glass panel for the building industry that is

easy to make and to mount to metallic doors or windows for shielding electromagnetic waves.

It is a further object of the present invention to provide a glass panel for the building industry that is aesthetically valuable and does not have the drawbacks of the panels according to the prior art, in which the problem of oxidation arises.

These and other objects are achieved by the method according to a first aspect of the invention that comprises a step of making a glass panel for the building industry having inside for all its extension at least a conductive layer. The conductive layer is a net made of a material comprising an inoxidizable metal chosen among gold, platinum, rhodium, cobalt.

According to a first embodiment, the net is made by woven wire, wherein the wire has a metallic or non- metallic core plated with highly conductive metals chosen among gold, platinum, rhodium, cobalt. Alternatively the wire can be of stainless steel with good electrical conductivity.

Being the woven net made of wire plated with a precious inoxidizable metal, there is at the same time the advantage of not requiring a step of superimposing to the net a protective film and therefore without further costs.

The maximum distance between two lead wires of the net is preferably 100-500 whereas the diameter of the wire is advantageously set between 20 and 100p. Therefore, since the net is woven very finely and with intrinsically coloured precious metals there is a remarkable esthetical effect.

Also the advantage of low costs is remarkable. The cost of the net plated with precious metal can be for example 10 times more than that of the net not plated, but a hundred times less than the cost of the net made

directly with a wire completely of the chosen precious metal.

According to a second embodiment, the net is formed by etching the glass surface forming a net of thin grooves, filling the grooves of a conductive material such as a metal or a metallic salt. Alternatively, the grooves may be filled of conductive layer that is then plated by conductive metals. Said conductive material may be chosen among gold, platinum, rhodium, cobalt, titanium, stainless steel. Said conductive material may be chosen among silver, silver nitrate (AgNO3), tin, copper. Means are provided at the border of the glass for contacting the net and grounding it through a window or a door frame.

According to a third embodiment of the invention, the conductive net is formed by depositing on the glass a net by a conductive material. Preferably a net is printed on the glass by a printing member wet by a first solution capable of binding a conductive material to the glass; then, a second solution containing a conductive material is spread on the glass, whereby the conductive material adheres only to the net and not to the glass and a conductive net is obtained printed on the glass.

Advantageously, the first solution comprises tin chloride and the second solution comprises silver nitrate (AgNOa) in the presence of a organic or inorganic reducing substance. On the resulting dried conductive net layer a metal such as gold, platinum, rhodium, cobalt, titanium, stainless steel may be plated. Means are provided at the border of the glass for contacting the net and grounding it through a window or a door frame.

The method for shielding according to the invention allows the achievement of all the above objects.

Under another general aspect of the invention a glass panel for the building industry impermeable to

electromagnetic waves is formed by at least a glass sheet associated to at least a layer of net of conductive material that extends for all its surface. The net may obtained by an embodiment of the method as above summarised.

The net of lead wire is advantageously located between two parallel sheets of glass. The two sheets of glass can be separated by an air chamber defined by a spacing frame, and the net of lead wire can be attached to one of the two sheets or to both.

In the first embodiment, not all the net is comprised between the two sheets of glass, and precisely an edge of net protrudes from all the sides of the panel and is suitable for contacting directly the metal body of the door or window to which it is mounted. The net edges that protrude from the panel are electrically not insulated. When mounting the panel in a recess of a door or window, it is possible to have the protruding net edges contact the metal body of the door or window, for example made of aluminium. This way the door or window form with the nets of the glass panels a single conductor, grounded by means of the grounding of the door or window same. The net edges that protrude from the panel before being mounted to the door or window are advantageously folded in order to form a tubular net, which in step of production can be filled with a resilient element, for example a spongy resilient material. This way, by arranging the panel in a door or window housing the tubular net portion that extends about all the panel is squeezed in the housing of the door or window and contacts continuously with it owing to the resilient pressure of the spongy material.

Adjacent panels can have respective edges that directly contact electrically each other.

Advantageously, the uncovered net edges can be coated with conductive paste, for example based on powder of graphite, copper, silver, aluminium in order to assuring a contact also where a distancing is present.

According to another aspect of the invention, a lead wire suitable for being used for an embodiment of the shielding panel can be formed by a continuous wire core with the function of support and at least a layer of plated metal on the wire core. The plated metal can be a inoxidizable metal chosen among gold, platinum, rhodium, cobalt.

The continuous wire core can be chosen among: -a wire containing conductive ; -a wire of conductive metal ; -a wire of not conductive material coated by means of vapour plating with a layer of conductive material; -a wire of nylon coated of silver by means of vapour plating; -a wire of nylon coated of silver by means of passage of the wire of a aqueous solution of AgN03 in presence of a organic or inorganic reducing substance.

The wire core, in a of the types above listed, is a lead wire and can be plated with a inoxidizable metal by means of galvanic techniques.

Brief description of the drawings Further characteristics and the advantages of the method for shielding glass surfaces of buildings from electromagnetic waves and of the glass panel for the building industry that carries out this method according to the invention will be made clearer with the following description of an embodiment thereof, exemplifying but not limitative, with reference to attached drawings, wherein: -Figure 1 shows a door or window metal with the glassed portion formed by four panel according to the invention; -figure 2 shows a portion of net obtained by means of

weaving conductive metal wire and the maximum distance between the meshes of wire; -figures 2A and 2B show two embodiments of wire that can be used to make the net of figure 2; -figure 3 shows a cross sectional view of a glass panel for the building industry comprising the shielding net according to the invention; -Figure 4 shows an exploded view of the panel of figure 3; -figure 5 shows an assembled view of the panel of figure 4 with the net edges protruding from the periphery; -figure 6 shows the panel of figure 5 with the protruding net edges wound as a tubular shape; -figure 7 shows the panel of figure 6 in an introduction step in the frame of a door or window; -figure 8 shows a different embodiment of a glass panel on which a net either is etched on the glass and then filled with conductive material or deposited on the glass; -figure 9 shows a different embodiment of a glass panel on which conductive layer is deposited on the glass.

Description of a preferred embodiment With reference to figure 1, a door or window 1 with electromagnetic shielding according to the invention comprises an outside frame 2, for example formed by aluminium sections, and a plurality of shielding panels 3, one of which is shown in position not yet mounted.

The outside frame 2 defines then four rectangular open frames made of conductive material.

As described hereinafter, according to a first embodiment of the invention, the panel 3 comprises inside a shielding net 4 of lead wire having edges 5 protruding from it and capable of contacting the metal frame 2 of the door or window 1.

The shielding net 4 is made of woven lead wire 6

(figure 2). The wire 5 of net 4 is formed by wire 5 in fibres or in metal plated with highly conductive metals, chosen among precious inoxidizable metal such as gold, platinum, rhodium, cobalt. Alternatively the wire 5 can be of stainless steel with good electrical conductivity.

The diameter of the wire 5 is advantageously set between 20 and 100p. In a preferred way, the wire has diameter set between 30 and 50p.

The net 4 allows an appropriate shielding from electromagnetic waves towards/from rooms closed by doors or windows like those shown in figure 1. The minimum thickness of the wire, for example 35 micron, and an appropriate size of the mesh of the net, for example 150- 500 micron, so that net 4 is enough permeable to light this like a slightly smoked glass. This way there is the possibility of illuminating the rooms with sunlight and to obtain at the same time a attenuation of entering sunlight same.

The wire 5, that may be of gold, titanium, cobalt, platinum, rhodium, since these metals may be alloys comprising coloured known metals, allow a remarkable esthetical effect owing also to the fine thickness of the wire 5 same.

The fact that the wire 5 is plated is remarkably not expensive. In fact, the cost of the plated net with precious metal can be for example ten times more than the net not plated, but a hundred times less the cost of the net executed directly with a wire completely with the precious chosen metal.

As shown in figure 2A, the lead wire 5 for example can be formed by a continuous wire core 5a with the function of support and at least a layer 5b of metal plated on the wire core 5a. The plated metal 5b, as already said, can be gold, platinum, titanium, rhodium,

cobalt.

The continuous wire core 5a can be in particular a wire containing conductive fibres or a wire of conductive metal, for example steel.

In the case the wire 5a is not a conductor, it can be advantageously covered by means of vapour plating with a layer 5c of conductive material. In particular, the wire core 5a can be a wire of nylon coated of silver 5c by means of vapour plating, in turn plated with an inoxidizable metal 5b by means of galvanic techniques.

The wire 5a, in case is of not conductive fibres, for example nylon, can be coated of the layer of silver 5c by means of passage of the wire 5a in a aqueous solution of AgN03 in presence of a organic or inorganic reducing substance. The solution of AgN03 can be complexed by addition of NH3. During the passage of the wire in the solution of AgNO3 gradually a reducing substance is added, that can be for example: -ipophossite of alkaline metals, -sulphite of alkaline metals, -sodium borum hydride, -hydrochinone, -a carboxylic acid.

With reference to figures from 3 to 6, a panel 3 is formed by a first glass sheet 11, a second glass sheet 12, a distancing frame 13 that form a air chamber 14. The net 4 is located between the sheet 11 and the frame 13.

Alternatively, net 4 can be located between the sheet 12 and the frame 13 or can be stretched between the two sheets of glass 11 and 12 by means of two frames as shown in figure 7.

With reference to figure 3, or to figure 7, the outer edge 6 of net 4 can be wound as a tubular net. For graphic simplicity, the circular cross section of the wire

has been accentuated. It is apparent that the production of the tubular net comprises 25 to a hundred wires for each centimetre of cross section.

The form of tubular curl of the edge 6 is advantageous for its elasticity and commodity of application in the introduction the panel in the recess of a door or window (fig. 1). In fact, the curl 6 has an own elasticity whereby it maintains completely in contact with the internal walls of the recess of the door or window. for accentuating this elasticity, the curl 6 can be filled of resilient gummy or spongy material, which is compressed without effort and maintains elasticity bringing in contact the net of the curl with the recess of the door or window.

With reference to figure 8, the net 4 can be alternatively formed by etching the glass surface of panel 12 forming a net of thin grooves. These grooves may then be filled with a conductive material such as silver, silver nitrate (AgN03), tin, copper. Then, a metal such as gold, platinum, rhodium, cobalt, titanium, stainless steel may be plated on the silver or silver nitrate.

Always alternatively, with reference again to figure 8, the net 4 is formed by printing or depositing on the glass a net by a conductive material by a first solution comprising tin chloride; then, a second solution containing a conductive silver nitrate (AgNO3) and a reducing substance such as CA (OH) z is sprayed on the glass. The glass panel has been advantageously washed by cerium oxide and distilled water. This method is analogue to that used for making mirrors. On the resulting dried conductive net layer a metal such as gold, platinum, rhodium, cobalt, titanium, stainless steel may be plated.

An etched film may be used alternatively to printing for depositing the tin chloride on the glass in order to

spread it according net-like.

Instead of printing the net, with reference to figure 9, a continuous layer of silver may be deposited if the tin chloride is fully spread on glass panel 12, and not with a net pattern. In this case, the resulting glass is transparent enough if the second solution of silver nitrate (AgNO3) and a reducing substance are sprayed in a controlled manner in order to assure a electrical conductivity. The optimum result is achieved by controlling the electrical conductivity during the spraying step.

The foregoing description of a specific embodiment will so fully reveal the invention according to the conceptual point of view, so that others, by applying current knowledge, will be able to modify and/or adapt for various applications such an embodiment without further research and without parting from the invention, and it is therefore to be understood that such adaptations and modifications will have to be considered as equivalent to the specific embodiment. The means and the materials to realise the different functions described herein could have a different nature without, for this reason, departing from the field of the invention. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.