GB2240782A

GB2240782A - Housing material for a portable communication device

Info

Publication number: GB2240782A
Application number: GB9102919A
Authority: GB
Inventors: Hiroji Kitagawa
Original assignee: Kitagawa Industries Co Ltd
Current assignee: Kitagawa Industries Co Ltd
Priority date: 1990-02-13
Filing date: 1991-02-12
Publication date: 1991-08-14
Anticipated expiration: 2011-02-12
Also published as: DE4104038A1; GB9102919D0; DE9101511U1; JPH03235398A; GB2240782B

Abstract

A material for constructing a housing for a portable communication device, such as a mobile telephone, comprises a synthetic resin containing carbon fiber developed from the vapour-phase pyrolysis of a hydrocarbon in the presence of ultrafine particles of a high-melting metal and/or a compound thereof. The carbon fiber is endowed with superior mechanical properties including tensile strength and high conductivity. The housing produced can shield electronic parts, oven in the outdoors or in an automobile or an airplane, from electromagnetic wave noise. Further, being light in weight, the housing enables a portable communication device to be easily carried and is difficult to break.

Description

I- AI C-P 2 7- HOUSING FOR A PORTABLE COMMUNICATION DEVICE This invention

relates to a housing for a portable communication device such as a portable telephone.

Currently, electronic devices equipped with electronic parts including microcomputers have been produced in large amounts to be used for various communication devices, automobiles, and the like. The number of the microcomputers used for these devices has been increasing and frequency of the microcomputers has become higher In these years, portable communication devices portable telephones and a telephone mounted on an (referred to as "a mobile telephone") have been the clock and higher. such as a automobile remarkably developed and used in general because of their smaller sizes.

Yet, the portable communication devices have problems. Since often being used in the outdoors or in transport vehicles such as automobiles and airplanes, the portable communication devices may be adversely affected by electromagnetic wave noise. When this happens, satisfactory communication by the portable communication devices cannot be realized.

Specifically, electronic parts of the portable communication devices, including portable telephones, may be broken, out of order, or wrongly operate due to the electromagnetic wave noise transmitted from the outside of the communication devices or generated in the electronic parts accommodated in the portable communication devicest 1 because the electronic parts are driven and controlled by weak electric currents. The electromagnetic wave noise flows in signal conductors or directly, affects the electronic parts. Among the electronic parts, a magnetic recording element is more frequently affected by the outside electromagnetic fields caused by a magnet or the like, and then information recorded in the magnetic recording element may disappear. This is because the magnetic recording element is made of a magnetic substance magnetized to have a high density with a small amount of energy.

To prevent the problems caused by electromagnetic wave noiser related-Art housings for accommodating electronic parts made of metal with high conductivity such as iron or housings made of synthetic resin containing carbon black particles as a conductive filler have been proposed. These housings can electromagnetically shield the electronic parts from the outside.

However, to solve the problems due to electromagnetic wave noise is more important in electronic parts accommodated in a portable communication device used in the outdoors, in an automobile or an airplane than those accommodated in other devices. In addition, the portable communication device has to be light in weight and built strong enough to be habitually carried.

The housing for electromagnetic shielding made of synthetic resin containing carbon black is light in weight; but, the amount of the carbon black should be adjusted such that the strength of the base material synthetic resin will 2 :1 1 i 1 1 not be deteriorated. Since the amount of carbon black has an upper limit to maintain a specified strength of the housing, the electric resistivity of the housing does not become lower than a certain value. Therefore, such housings can not be endowed with both high durability and low electric resistivity, so that the housing is inappropriate for accommodating a portable communication device.

On the other hand, a housing for electromagnetic shielding made of iron is provided with both low electric resistivity and high permeability. The housing can shield electromagnetic wave noise generated in the electronic parts the thus preventing the breakdown or malfunction of the electronic parts. Yet, the housing cannot be light in weight because too thin a plating of iron is not strong enough to be used by itself as the housing for a portable communication device.

As described above, a housing for a portable communication device is subject to electromagnetic wave noise because the housing is often used in the outdoors or in an automobile, an airplane, or the like, which may be a source of electromagnetic wave noise. Therefore, the housing has to effectively shield electronic parts in the housing from electromagnetic wave noise. At the same time, the housing should be durable enough to be used in the outdoors or in an automobile or the like. Further, the housing should be light in weight to be easily carried.

Wherefore, the object of this invention is to provide a 3 and low-frequency magnetic fields caused by a magnet oi like - 4 housing for a portable communication device that can effectively shield electromagnetic wave noise and is durable and light in weight.

According to one aspect of the present invention there is provided a material for constructing a housing for a portable communication device which protects the communication device against magnetic and electromagnetic interference comprising a synthetic resin containing carbon fibers developed from ultrafine particles.

Preferably the carbon fibers are developed from ultrafine particles of a high-melting metal and/or a compound of the high-melting metal yielded by a vapour-phase system for thermally decomposing hydrocarbon.

According to other aspects of the present invention there are provided a housing, a portable communication device and a method of making the material.

The housing for a portable communication device of this invention may be made of synthetic resin, for example, polyester resin, vinyl resin, and polyamide resin, reinforced by a specified carbon fiber.

Unlike polyacrylonitri 1 e carbon f iber and pi tch carbon f iber, the carbon fiber used in this invention can be formed in a whisker shape, having a micro-diameter almost the same as that of ultrafine particles of a high-melting metal and/or a compound of the high-melting metal. The carbon fiber can be securely adhered to the base material synthetic resin and can be uniformly dispersed all through the synthetic resin such that the carbon fibers are interlaced, entangled and contact one another. Therefore, the housing made of synthetic resin I i i containing the carbon fiber can effectively prevent electromagnetic wave noise from entering the housing in any direction.

Further, the carbon f iber used in this invention may be composed of layers of regular crystals of graphite, and provided with the lowest electric resistivity; that is, the highest electric conductivity, among all kinds of carbon fiber. The carbon fiber also has superior mechanical properties such as high tensile strength inherent to all kinds of carbon fiber. Accordingly, the carbon fiber uniformly dispersed and retained in the base material synthetic resin provides the housing with high conductivity and superior mechanical strength. The housing endowed with conductivity reflects or absorbs the electromagnetic noise from the outside and electromagnetically shields the inside of the housing from the outside.

The degree of conductivity, that is, electrical resist ivity, can be determined by the amount of the carbon fiber contained in the base material. The more carbon fiber is contained in the base material, the more frequently the carbon fiber contacts one another. When the carbon fiber is contained in large amount so that all the carbon fiber are kept in contact with one another, the electrical resistivity of the housing becomes almost the same as that of the carbon fiber.

The content of the carbon fiber in the synthetic resin should be above 20% by volume of the synthetic resin to reduce the electrical resistivity of the housing, preferably between 30% and 50% by volume of the synthetic resin.

The high-melting metal could be vaporized at between 950 OC and 1300 C, the temperature range in which the hydrocarbon is thermally decomposed. Applicable for use as the highmelting metal is titanium (Ti), zirconium (Zr) or the like in group IVa according to the periodic system, vanadium (V), niobium (Nb) or the like in group Va, chromium (Cr), molybdenum (Mo) or the like in group VIa, manganese (Mn) or the like in group VIIa, or iron (Fe), cobalt (Co) or the like in group VIII. Metals Fe, Co, Ni, V, Nb, Ta, Ti, and Zr are most preferable. Oxide, nitride, chloride or the like of the high-melting metal can be used as the high-melting metal compound.

Reference will now be made, by way of example, to the accompanying drawings, the single figure of which illustrates a portable telephone embodying the present invention.

The figure shows a portable telephone 1 embodying the present invention. The portable telephone 1 has a housing 5 comprising a receiver 2 and a transmitter 3. Between the receiver 2 and the transmitter 3 plural pushbuttons 4 are arranged. on the inner surface of the housing 5 a metallic layer 8 is formed such that the portable telephone may not be influenced by low-frequency magnetic fields caused by magnets or the like. Further, the portable telephone 1 has various electronic parts 6, a battery 7, and such, in the housing 5.

6 -11 The housing 5 is made of ABS resin, nylon including' 66nylon, or another similar material. Preferable is a mixture of 65% by volume of ABS resin and 35% by volume of carbon fiber.

The housing 5 is manufactured as follows.

Using a vapour-phase system for thermally decomposing benzene in a furnace of 950 'C through 1300 OC, carbon fiber having a diameler- of between about 0.1pm and 0.5pm and a length of between about O.lmm and lmm are developed from iron powder having a diameter of between about 0.02pm and 0.03pm. The housing 5 is then moulded to be 2mm in thickness from ABS resin containing the above carbon fiber by injection molding or vacuum molding.

The metallic layer 8 is about 0.02mm in thickness and is made of nickel (Ni) or iron (Fe) applied to the inner surface of the housing 5 by vacuum evaporation, electrolysis plating, electroless plating, coating, or the like.

The portable telephone 1 having the housing 5 mentioned above in which the electronic parts 6 are accommodated produces the following effects.

The portable telephone 1 is endowed with higher conductivity than that of a conventional portable telephone because of the carbon fiber. Electromagnetic wave noise is effectively reduced even when the portable telephone 1 i used in the outdoors where the portable telephone 1 subject to electromagnetic wave noise, or in an airplane or the like where the portable used near a source of electromagnetic wave noise Since the portable telephone 1 is strongly 7 is an automobile, telephone 1 is constructed in spite of its lightness, the portable telephone 1 is convenient to be carried and is difficult to break during use, even in the outdoors.

Further, the metallic layer 8 formed on the inner surface of the housing 5 in the portable telephone 1 made of nickel or the like can effectively shield low-frequency magnetic waves caused by a magnet and the like. The electronic parts 6 accommodated in the housing 5 are, therefore, prevented from being broken and malfunctioning.

The ABS resin containing the carbon fiber can be molded easily in any shape because the carbon fiber is a short fiber having a lengthr about one hundred times as long as its diameter. Accordingly, although the housing 5 of the portable telephone 1 has a complicated shape, the housing 5 can be manufactured to have a desired thickness and shape and uniform local strength by injection molding or the like.

Although an embodiment of the present invention has been explained, the invention is not to be limited to the embodiment illustrated and described For example, the invention can be applied to housings for other portable communication devices including a mobile telephone, as well as the portable telephone 1. Further, in addition to the ABS resin and nylon, the carbon fiber can be contained in various kinds of resin.

8 -A-

Claims

A material for constructing a housing for a portable communication device which protects the communication device against magnetic and electromagnetic interference comprising a synthetic resin containing carbon fibers developed from ultrafine particles.
2. A material according to claim 1, wherein the carbon fibers are developed from ultrafine particles of a high-melting metal.
3. A material according to claim 1 or claim 2, wherein the carbon fibers are developed from ultrafine particles of a compound of the highmelting metal by a vapour-phase system for thermally decomposing hydrocarbon.
4. A material according to any preceding claim, wherein the carbon fibers are above 20% by volume of the synthetic resin.
5. A Material according to any of cl.i',',iis 1 to 3, wherein the carbon 20 fibers are between 30% and 50% by volume of the synthetic resin.
6. A material according to any preceding claim, wherein the high melting metal is selected from the group consisting of titanium (Ti), zirconium (ZO in group IVa according to the periodic system, vanadium (V), niobium (Nb) in group Va, chromium (Cr), molybdenum (Mo) in group V1a, manganese (Mn) in group V11a, and iron (Fe), cobalt (Co) in group VIII.
7. A material according to claim 6, wherein the high-melting metal is selected from the group consisting of Fe, Co, Ni, V, Nb, Ta, Ti and Zr.
8. A material according to any of claims 3 to 6, wherein the compound is selected from the group consisting of oxides, nitrates, and chlorides.
9. A material according to any preceding claim, wherein the synthetic resin is selected from the group consisting of ABS resin and nylon.
10. A material according to claim 9, wherein the nylon includes 66 nylon.
11. A material according to any preceding claim, wherein the carbon fibers have a diameter of about 0.1pm to 0.511m and a length of about 0AMM to lmm.
12. A material substantially as described with reference to the accompanying drawings.
13. A housing for a portable communication device which protects the communication device against magnetic and electro-magnetic interference comprising a hollow shell being of a material according to any of the preceding claims.

- 11
14. A housing according to claim 12, additionally comprising a shielding lining of metal deposited on an inner surface of the housing.
15. A housing according to claim 13, wherein the shielding lining of a metal is approximately 0.02mm in thickness and made of a metal selected from the group consisting of nickel (Ni) and iron (Fe).
16. A housing substantially as described with reference to the accompanying drawings.
17. A mobile telephone or like portable communications device having a housing as claimed in any of claims 13 to 16.
18. A mobile telephone substantially as described with reference to 15 the accompanying drawings.
19. A method of making a material as claimed in any of claims 1 to claim 12.

Published 1991 atThe Patent Office. State House. 66171 High Holborn. London WC I R 477. Further copies may be obtained from Sales Branch. Unit 6. Nine Mile Point Cwmfelinfach. Cross Keys. Newport. NPI 7HZ. Printed by Multiplex techniques lid. St Mary Cray, Kent.