FR2484397A1 - Safety glass for microwave appts. - with impermeable conducting barrier formed by metallic mesh - Google Patents

Abstract

A safety glass for microwave or hyper-frequency appts., used as a partition, door or chamber, esp. for microwave ovens, includes an impermeable conducting barrier which annihilates all emission of microwaves outside the oven. The glass consists of a sheet of glass, a conducting network formed by a metallic mesh, e.g. of Pt, Au or Ag, and a protective enamel layer. The glass may be made by prepg. a mesh screen, coating this with photo-sensitive varnish, arranging this in place, irradiating with ultraviolet irradiation, and removing the unexposed parts of the screen, e.g. by washing with water under pressure. The screen is used in the enamelling of the glass, and the assembly is finally coated with an enamel, pref. transparent, dried, baked to fuse the enamels and pyrolyse organo - metallic cpds., and tempered by rapid cooling.

Description

 The invention relates to a safety glass for microwave or microwave apparatus used as a partition, door, enclosure, in particular microwave ovens.

 Many industrial and domestic appliances such as ovens using microwaves or microwaves allow a certain heating. In fact, it has been observed that an electromagnetic wave, propagating in an environment whose dielectric constant is very much smaller than one, causes the water molecules of the material to vibrate, causing the latter to heat up. These microwaves propagate like other electromagnetic waves. They are transmitted, reflected or absorbed depending on the substance encountered. Microwaves, on the other hand, pass through air and most materials but are stopped by the metal that reflects them.

Using this phenomenon, microwave ovens have been produced, in particular for cooking, composed of a cooking enclosure hermetically closed by a door and a wave generator such as a magnetron.

The enclosure consists of metal walls, in particular stainless steel and the door is also made of steel provided with a porthole lined with a finely perforated metal wall. The magnetron, powered by an electric current, transforms electrical energy into electromagnetic energy distributed in the enclosure thanks to the slow and regular rotary movements of an agitator. When a food is placed in the oven, the waves emitted cause a change of orientation of the water molecules which rotate on themselves by 180 degrees, then return to their initial position. These extremely rapid changes in orientation (of the order of 2,450 million times per second) cause friction inside the food resulting in heating and, consequently, cooking of the food.

 However, microwave frequencies have a harmful influence on humans and, in particular, may cause burns or localized destruction of tissue. Lower value microwaves present less risk but they can be harmful to pacemakers and mechanical implants worn by certain subjects. Fields can indeed damage the former and create unbearable heating of the latter.

 Therefore, people, devices and the environment must be protected by shields, protection and detection devices.

With regard to microwave ovens, an enclosure with metal walls has been produced provided with a door consisting of a stainless steel plate pierced with holes of the order of four millimeters in front of which is another transparent plastic plate.

However, this solution is complex, therefore expensive and does not allow observation inside the oven.

 The present invention aims to remedy these drawbacks and proposes to provide a safety glass, resistant and transparent, having conductive properties allowing the capture of electromagnetic radiation and its elimination to ground. The glass, according to the invention, seals against radiation using the process known as the Faraday cage.

 To this end, the invention relates to a safety glass for microwave or microwave device used as a partition, door, enclosure, in particular microwave ovens, characterized in that it comprises an impermeable conductive barrier annihilating any microwave emission to the outside of the oven.

 The invention will be better understood by referring to the following description given by way of nonlimiting example and to the attached drawing in which - Figure 1 is a perspective view of a glass according to the invention provided, according to a first embodiment of a conductive network - Figure 2 is a perspective view of a glass according to the invention provided, according to a second embodiment, a laminate containing a conductive grid.

 We refer to Figure 1.

The glass consists of a glass plate 1, a conductive network 2 formed by a metal mesh and a layer of protective enamel 3. This glass is produced according to the following procedure - the grid, the design of which is reproduced on a screen-printing screen, is obtained either by cutting an inactinic paper, or by the transfer of an existing frame.

 The screen, previously coated with a photosensitive varnish, is then plated on the artwork made according to the description above. After irradiation with ultraviolet rays, the unexposed parts of the seat Elimrleess screen, in particular by washing with water under high pressure.

 The screen, on which the grid 2 has been reproduced, is then used for enamelling glass pieces 1 intended for the manufacture of partitions, doors, enclosures protecting from electromagnetic radiation.

 The metals, the conductive properties of which may be used for this application, are inter alia platinum, gold, silver existing in the form of resinates. Poorly oxidizable metals, such as nickel, chromium can also be used. Of course, this list is not exhaustive.

The protection of the mesh thus produced is obtained by a layer of transparent or colored enamel 3, deposited on the mesh 2.

 The whole is then dried in order to favor the departure of the solvents contained in the pastes of the metallic compositions or enamels.

After drying, the glasses are placed in an oven to obtain the melting of the enamels and the pyrolysis of the organometallic compounds.

 Rapid cooling then allows the tempering of the glass parts, giving them increased mechanical and thermal properties, as well as safety in the event of accidental breakage of these glass parts.

 We refer to figure 2.

According to another embodiment, the glass consists of a first glass plate 4 and a second glass plate 5. Between these glass plates 4 and 5 is disposed a laminate 6 containing a conductive mesh.

 The glasses 4, 5, intended for assembly, are cleaned with alcohol and then dried. The laminate is either a gauze made of metallized synthetic threads such as polyester mylar, or a fine metallic mesh of stainless steel. The assembly is obtained by bonding with an adhesive polymerizing with ultraviolet rays - whose refractive index is close to that of glass to benefit from satisfactory transparency.

Provision is made in the glasses, produced according to one or other of the methods described above, for unprotected conductive pads to allow the devices to be earthed or grounded.

 In addition, conductors can be taken advantage of to ensure the operation of any type of security for devices protected or equipped with partitions, doors, enclosures made from safety glass according to the invention.

 Although the invention has been described with regard to a particular embodiment, it is understood that it is in no way limited thereto and that it is possible to make various modifications to it in terms of shape, structure and combinations. of these various elements without thereby departing from the scope and spirit of the invention.

Claims (6)

Claims 1. Safety glass for microwave or microwave device used as a partition, door, enclosure, in particular microwave ovens, characterized in that it comprises a conductive waterproof barrier (2) annihilating any emission of micro- waves to the outside of the oven. 2. Safety glass according to claim 1 characterized in that the conductive impermeable barrier is a conductive network formed by a mesh (2) integral with the top of the glass (1) and covered with a layer of enamel (3).  3. Safety glass according to claim 1 characterized in that the conductive impermeable barrier is a laminate (6) containing a conductive mesh disposed between two glass plates (4), (5):  4. A method of manufacturing a safety glass according to claims 1 and 2 and comprising uh conductive network characterized in that one reproduces, either by cutting an inactinic paper, or by transfer of existing frame, a drawing of grid on a screen printing screen; that a screen previously coated with a photosensitive varnish is placed on the artwork; that it is irradiated with ultraviolet rays and that the unexposed parts of the screen-printing screen are eliminated; that by means of the screen on which the grid has been reproduced, the enameling is carried out and then the mesh is covered with a layer of enamel, preferably transparent; that the assembly is then dried and then placed in an oven for melting enamels and pyrolizing organo-metallic compounds; and finally, one proceeds to quenching rapid cooling.  5. A method of manufacturing a safety glass according to claims I and 3 and comprising a laminate containing a conductive grid, characterized in that the glasses intended for assembly are cleaned with alcohol and then dried. these glasses; that is placed between these glasses, either a gauze made of metallized synthetic threads such as a polyester mylar, or a fine metallic mesh of stainless steel; that the assembly is assembled by bonding using an adhesive polymerizing with ultraviolet rays. 6. Safety glass according to claims i and 2 characterized in that it comprises unprotected conductive areas for the earthing or grounding of the device.