METHOD OF PRODUCING A METALLIC LAYER ON THE SURFACE OF A DETAIL FOR SHIELDING AGAINST ELECTROMAGNETIC RADIATION

Abstract: The invention relates to a method of transferring a layer onto a detail (8) which shields against electromagnetic radiation. The layer (3, 7) is transferred with a predetermined extension directly or indirectly on to the detail (8) with the help of a known printing method.

Description: METHOD OF PRODUCING A METALLIC LAYER ON THE SURFACE OF A DETAIL FOR SHIELDING AGAINST ELECTROMAGNETIC RADIATION In our surroundings there are a large number of electromagnetic fields which are formed by electrical machines and electrical equipment, such as radios. TVs. refrig¬ erators, deepfreezes, stoves, electric ovens, computers, car- and pocket telephones, electrical conductors, power tools, lamps and a number of other devices. These electromagnetic fields, which surrounds us every day, probably cause a number of symptoms for people who are allergic to this radiation, in the form of different al- lergies. cancers of different types and other complaints. There are today different forms and methods for trying to reduce the effect of the electromagnetic field on people through different types of screening methods. The electromagnetic radiation can be reduced through shielding the radiating unit with a metallic casing, which can contain me electromagnetic field and thereby re¬ duce the risk of injury to people. These shielding devices can be made, for example, as an enclosing casing, formed of a net of metal wires or of a metallic foil or from a surface which is metallized through vacuum vaporisation or the structural plastic material in the device can be completely or partially mixed with metal fragments. The protective effect is thus achieved through placing an obstacle in the radiation direction which shields at least at the place where it is desired to avoid radiation from the electromagnetic field or to shield larger surfaces than that. To produce this shielding is often expensive and complicated and sometimes does not give an estheticallv attractive result. To shield, for example, through clothing the eiectncal devices with a net or foil does not look nice and furthermore makes it dif¬ ficult to operate and access them. Internal solutions, such as foils moulded-in or mechanically mounted become both expensive and complicated. If a surrounding casmg of plastic is constructed with an electrically conductive material baked into d e plastic then the casmg becomes unnecessarily heavy and furthermore expensive to produce, smce the mateπal cost becomes high and the operating time in an lnjec- tion mould takes a long time. A vacuum vapoπsatton method is suitable for produc¬ ing a surface coating of a thin metallic layer. This method causes problems in the form of difficult handling. First the details must be unpacked. Then comes masking of surface which it is not desired to coat with metal, then hanging up on different stands and then introduction into the autoclave which is then evacuated of air m or- der to produce a vacuum. It is only after this that the metallization through vacuum vapoπsation can take place. Thereafter follows demounting of the metallized details, which will be packaged and transported to the manufacturer of the eiectncal de¬ vices. Vacuum vaporisation plants costs many millions of Swedish crowns which adds to the cost for each metallized detail. Metallization which is performed with anodisation has similar disadvantages as the vacuum vaporisation method. All the above described methods are both time-consuming, labour-intensive and ex¬ pensive at the same time as the quality of the metallic layer developed is not always sufficiently good. The present invention is intended to solve the above mentioned problems. It is known in the pnor art to transfer a non-cured or undried paint substance to a foundation from a stamp pad which can be coated with paint m different ways. For example the pamt can be pressed through a template against a plate where a picture is etched with the exact shape, spread, thickness and colour. A soft and pliable stamp pad men gets this picture through bemg pressed agamst this surface and then transfers this to a pre-determmed place on a surface of a detail, for example, a pen. a clockface. a toy or some other detail surface, which can be arched, curved or have another simple surface shape The picture can also be taken from a screen printed picture The stamp pad is shaped so that it can follow the different shaped surfaces so that the picture is transferred and covers m the best way the whole of its surface so that no part of me picture is left out This method is known as " 'tampon-pπnnng " According to the mvention the advantages of tampon-pnntmg can be used through exchanging the printing ink for a metallic matenal which then forms a shielding layer against electromagnetic radiation. According to the mvenπon masking of sur¬ faces which are not to be metallized, for example, the front side, me making of holes, fittings, join surfaces etc. becomes unnecessary as the shape, thickness and extension of the print is regulated exactly with this tampon-pnntmg method. Ac- cordmg to the invention, by further refining this known prmtmg method, much more complicated surface shapes can be coated with a metallized layer so that even ex¬ tremely arched and complicated surfaces with projecting elements or fittings and me like can be coated. The stamp pad can m this case be shaped more exactly so that it m general fits the detail which is to be coated with a layer. One can m this case produce the stamp pad in an extra soft and flexible matenal so that it can stretch itself into the smallest nook. Smaller details with extremely complicated shapes, for example, car telephone cases, become easier to coat with a layer since the tampon-printing method according to the invention is especially easy to perform on small surfaces. All handling such as placing in or removing out of details for metallization in a vacuum vaponsation method does not have to be performed ac¬ cording to the mvention. Injected moulding plastic matenal with a metal mixed in does not need to be used either. Instead, according to the mvention, the structural material which normally is needed for the purposes is used. To place m or glue fast a metal casing also becomes unnecessary, as well as making of different types of nets According to the present mvention a cheap, quick and particularly easy method of obtaining a metallic layer as a shield agamst electromagnetic radiation on a detail which is to be used m a eiectncal device is provided. Furthermore the method ac- cordmg to the mvention gives an extremely high quality result Accordmg to the invention the metallic layer is transferred with a pre-determined spread directly or indirectly on to the actual detail with the help of a known printing method. As a printing method can be used, for example, a photographic method m order to pro¬ duce an exactly shaped picture. This picture is then transferred through etching to the surface on a plate. It can also be transferred to a screen frame. A metallic mate¬ rial is then laid out as a thin layer on the etched plate or pressed through the screen frame out onto a foundation. The now printed metal layer is then collected by a tampon stamp pad which then transfers this to, for example, a casing for a car tele¬ phone. Application of this metallic layer according to the invention only takes a few seconds. This must be compared with the vacuum vaporisation method, which is up to now the most successful form, for example car telephone casings, which requires masking devices which are large, clumsy and difficult to handle, and which can only be delivered after several days, which is extremely time-consuming. Naturally all the surfaces of the metallic layer according to the invention do not have to be tampon printed at the same time. The same detail can be printed more than one time in different places. With small series or in the case that the details are small, it is most profitable to use smaller tampon printing pads and printing machines. With large series, and in the case large bits should be coated, according to the invention, it is more profitable to have less prints per detail with larger pads and larger machines. The invention is described more closely below with the help of some preferred ex¬ amples of embodiments with reference to the appending drawings in which Fig. 1 shows a perspective view obliquely from below of a tampon printing pad which is coated with an exactly shaped formation of a metallic layer which lays on its surface and which is to be transferred to the casing of, for example, a pocket telephone and Fig 2 shows a partial perspective view of a detail coated with the exact prmtmg pattern of a metallic layer The mvennon is applied accordmg to fig 1 by a preferably soft and resilient tampon prmtmg pad having been used in the prmtmg method which is used for the transfer¬ ring of a metallic layer on to the actual detail 8, which pad 1 has a predetermined tailor-made shape, so that it m the mam fits, for example, a casmg for a pocket tele¬ phone The tampon prmtmg pad 1 is coated with an electncally conductmg metallic layer on its surface 3, which extends on chosen places, thus not too close to a dis- play 2 or interconnection means 2' or too near to the hole edges for the number buttons 2" or where the fittings 2"' are made This layer 3 is transferred from a preferably etched plate surface The tampon prmtmg pad 1 can have different shapes with at least one non-flat surface 5 m order to be able to transfer the layer 3 on to different shapes of surfaces which are found in, for example, a detail 8 in me shape of a telephone casmg. When the tampon prmtmg pad 1 is pressed against the detail 8, the metallic layer is printed on the predetermined places of the surface of the detail 8 Fig. 2 shows how it is possible to apply the mvennon so that the metallic layer 7 is printed by means of tampon printing pad on to the detail 8, whereby me metallic layer 3 ends up exactly m the chosen positions, which are, for example around a hole 10 m a recess 6 and along an arched edge, where an eiectncal conductor 9 is to be shielded against electromagnetic radiation Naturally, the detail 8 can appear m many different ways and be coated with metallic layers 7 of varying shapes and ap- pearances It is also conceivable that the metallic layer 3 can be transferred to the tampon prmtmg pad 1 m a different way, but preferably from an etched plate sur¬ face If the metallic layer is transferred with the help of a screen prmtmg method then it can naturally be printed directly onto the detail which shall be provided with this layer without, as is descnbed above, transferrmg the layer from a screen printed sur¬ face with a tampon prmtmg pad. Through producmg the screen frame and its cloth accordmg to the curved surface which is to be coated with a layer, with a predetermined pattern, it is possible to also coat differently shaped surfaces with a layer by screen prmtmg directly onto the detail Combinations of the above described printing methods for coating details with a layer which protects against electromagnetic radiation are also possible in order to apply the mvention. The layer coating can also be performed with help of a fluid, for example water, whereby for example a telephone casmg which is to be coated, is sunk in a water- bath whereafter the layer is pressed up against the surface of the casmg and fixes itself against it. This layer can be produced as a foil and can be connected to a telephone casing which is to be coated before the sinking in the waterbath takes place. In this case me foil fastens on to the telephone casing even if it has curved surfaces. In the tampon printing method described above, the plate which is provided with the pre-printed picture of electrically conducting pamt can be foldable so that during the transferrmg of the pamt to the plate it can have one shape, for example generally flat and when the tampon printing pad is to collect the pamt it can have another shape which fits the shape of the tampon printing pad. If the surface such as the intenor of a telephone case is curved and complicated then problems occur when printing the metallic layer m the most difficult to approach regions m me nooks and corners of the telephone casmg. If the pre-pnnted plate can be folded so that it is better adapted to the shape of the tampon printing pad then the electrically conductmg pamt can also more easily be transferred to the intended surfaces on the tampon prmting pad even if these are on an extremely curved surface. The metallic paint can then be pressed agamst the telephone casings with curved and complicated shapes

Claims: Claims 1 Method of placmg a layer (3, 7) on a detail (8). which shields agamst electro¬ magnetic radiation, characterised in that the layer (3, 7) with a predetermined ex- 5 tension directly or mdirectly is transferred by means of a known prmtmg method on to the detail (8) 2 Method accordmg to claim 1, characterised m that the prmtmg method for the transferring of the layer (3, 7) on to the actual detail (8) is tampon prmtmg, whereby 10 a prmtmg pad (1) made of a compliant matenal is used for the indirect transferrmg of the layer (3, 7) to the detail (8). 3 Method accordmg to claim 2, characterised m mat the layer (3, 7) is transferred mdirectly on to the detail (8) from an etched or screen printed surface by means of 15 the prmtmg pad ( 1 ). 4 Method accordmg to claims 2 or 3, characterised in that the printing pad (1) is formed with a shape which m general corresponds to that of the detail (8) for per¬ mitting the transferrmg of the layer (3, 7) on to a detail (8) having a complicated 0 shape 5 Method according to claim 4, characterised m that the prmtmg pad (1) is made in an extremely compliant matenal m order to transfer the layer (3, 7) for shielding agamst electromagnetic radiation on to the extremely uneven foundanon of a detail 25 (8) 6 Method accordmg to claim 1, characterised m that the prmtmg method for the transferrmg of me layer (3, 7) to the detail (8) is screenpnntmg, wherein the trans¬ ferrmg takes place directly on to the detail _5 0 7 Method accordmg to claim 6. characterised in that during the screenpnntmg, a screen frame is used, of which the screen cloth is shaped in order to fit an unevenly shaped surface of a detail (8) 8 Method accordmg to claim 1, characterised m that the prmtmg method for trans¬ ferrmg of the layer (3, 7) to the detail (8) is performed with the help of fluid form¬ ing a flmdbath, wherem the detail (8) which is to be coated with the layer (3, 7) is sunk into the flmdbath whereafter the layer (3, 7) is pressed up agamst the surface of the detail (8) and fixes agamst it

Inventors: ERIKSSON LARS, ERIKSSON, LARS
Applicants: ERICSSON TELEFON AB L M, ERIKSSON LARS, ERIKSSON, LARS, TELEFONAKTIEBOLAGET LM ERICSSON
Application year: 1997
Main classification: H05K9
IPC codes: G12B17, H05K1, H05K3, H05K9