Dielectric structures in connectors

Abstract: The invention relates to the use of a specific polymeric material for various dielectric structures in electrical connectors such as connectors for coaxial cables. These structures must on the one hand be able to withstand large forces both during mounting of the connector on the cable, provide a stable attachment of the various parts of the connector over wide temperature ranges and occasionally at the presence of various chemical agents and at the same time have appropriate electrical characteristics. Especially for high frequency connectors the dielectric constant of such structures must be kept sufficiently low in order to yield satisfactory high frequency transmission through the connector. The invention thus discloses the application of a specific material for these purposes and a connector in which this material has been applied.

Description: Technical Field The present invention relates to the use of polymer compositions comprising cycloolefin copolymer in insulators used in electrical connectors particularly in connectors for coaxial cables and furthermore to a coaxial connector comprising an interface insulator made of such polymer compositions. Background of the Invention In connectors of the above kind it is known to apply various supporting structures made of a suitable dielectric material for instance to fix the centre terminal of the connector appropriately within the main body of the connector, to transmit pressure between various parts of the connector during mounting of the connector on the cable and to act as a mechanical abutment or backstop for various displaceable parts of the connector. Both in use and during mounting of the connector these structures are very often exposed to large mechanical stress, which they must be able to withstand without unacceptable deformations or even destructions, often over a wide range of temperatures, humidities and even at the presence of chemical agents that may increase the risk of damage to the structures. Within the art it is known to apply for instance PEHD or TPX for such structures, but these materials suffer from a number of drawbacks such as being too soft to provide a consistent attachment of the centre terminal to the main body of the connector. A composition which could be used for instance for dielectric structures in electrical connectors is described in detail in US 6,008,306 which is considered to represent the closest prior art for claim 1, showing a large number of structural formulas for a cyclic polymerisable composition. Document US 4 662 693 which is considered to represent the closest prior art for claim 6, discloses a coaxial connector comprising a tubular support member, a tubular member for transmission of an axial force and a tubular bushing. Disclosure of the Invention Based on the above mentioned problems and disadvantages it is the object of the present invention to provide a material for said structures having superior characteristics compared with materials previously used. This object is attained by the application of an amorphous, transparent copolymeric materiel based on cyclic and linear olefins. A material of this kind will generally be referred to in the following by the abbreviation COC. A specific material of this kind is described and manufactured by Ticona GmBH and commercially available under the tradename "Topas ®" (Thermoplastisches Olefin-Polymer amorpher Struktur). Various parameters are important in connection with the above mentioned structures in a connector. Among these are the dielectric properties (dielectric constant) and the mechanical properties such as hardness, dimensional stability and Impact resistance. Furthermore a limited influence of chemical agents that could potentially be present in those environments in which the connector is used could be important. In use the various parameters must be kept within acceptable ranges as a function of temperature, relative humidity etc. From an electrical point of view it is desirable that the dielectric constant particularly of the support structure between the centre terminal and the main body of the connector be kept as low as possible as a large dielectric constant of the material of this structure will lead to a relatively high capacitance between the centre terminal and the main body thereby reducing the upper limiting frequency for signal transmission through the connector. For connectors used in high frequency transmission systems this factor is vitally important. The invention furthermore discloses a coaxial connector of the kind mentioned initially comprising a main body for connection to the outer conductor of a coaxial cable and a centre terminal for connection to the inner conductor of the cable. The dielectric support structure for attachment of the centre terminal the main body of this connector is according to the invention made of COC, but it is understood that other dielectric structures of the connector could also be made of this material. Typical parameter values of a material of the kind referred to above as COC for use in a various connectors are given in the detailed description together with an embodiment of a connector as mentioned above. The above mentioned objects are achieved by the features of Claims 1 and 6. Brief Description of the Drawings The invention will now be described in more detail with reference to the accompanying drawing, in which figure 1 shown a longitudinal cross sectional view of a coaxial connector in which dielectrics structures made of COC are applied. Detailed Description of the Invention With reference to fig. 1 there is shown a cross-sectional view of a coaxial connector as a non-limiting example of tne use of COC for the dielectric structures in a connector. The connector, generally identified by reference number 1, comprises the main body 2 which is electrically connected to the outer conductor 6 of the cable. This connection takes place via an electrically conductive ferrule 13 exerting a high pressure radially inwardly on both the outer conductor 6 and on the jacket 5 of the cable. As a mechanical backstop there is inwardly of the outer conductor 6 provided a tubular bushing 12 coaxial with the cable and made of a material of sufficient radial rigidity the withstand the pressure from the ferrule 13. Electrical contact between the ferrule 13 and the main body 2 is provided along the contact surface 14. The connector is furthermore provided with a centre terminal 4 to be connected electrically to the inner conductor 8 of the cable. This takes place via a hollow, tubular end portion 9 of the centre terminal 4 formed to be able to undergo a radial compression around the end of the inner conductor 8. The centre terminal 4 is kept in a fixed radial and axial relationship to the main body 2 by means of a tubular support member 10 made of a dielectric material. The radial compression of the end portion 9 of the centre terminal 4 is during mounting of the connector on the cable brought about by means of a tubular member 11 for transmission of axial force between the left (as seen in the figure) end of the bushing 12 and the conical end face 15 of the end portion 9 of the centre terminal 4. Thus an axial displacement of the bushing 12 causes a radial compression of the end portion 9 whereby a firm electrical and mechanical connection between the centre terminal 4 and the inner conductor 8 is obtained. Both during use and during mounting of the connector on the cable the dielectric components 10, 11 and 12 are subjected to large forces. There are a number of characteristic properties of dielectric materials for use in connectors of the kind described above. It is important to provide a material with a combination of a low dielectric constant, i.e. a dielectric constant relatively close to unity, and at the same time possessing the required mechanical characteristics relating to hardness, dimensional stability etc. Over the required ranges of temperature, humidity etc, and which can also stand the presence of various chemical agents present in the environment where the connector is to be applied. In a preferred embodiment of the connector according to the invention the initially mentioned COC material produced by Ticone GmBH under the tradename "Topas ®" and commercially available under a number of different types numbers covering different operational temperature ranges has been used for the tubular support member 10. The tradename "Topas ®" is an abbreviation for "Thermoplastisches Olefin-Polymer amorpher Struktur" (thermoplastic olefin-polymer of amorphous structure). A cycloolefincopolymere (COC) of said kind is generally defined by the chemical formula: The above material is characterised by a number of desirable properties both relating to mechanical and electrical (dielectric) characteristics. During construction of the connector as well as in practical use it is essential that the centre terminal 4 remains at a precisely fixed position coaxial within the main body of the connector. The material of the tubular support member 10 must ensure a high dimensional stability of this member over a wide temperature rang e. The above mentioned material has a sufficient dimensional stability to temperatures up to 170 degrees centigrade, which ensures that the centre terminal 4 will not undergo an unacceptable displacement in the support member 10. Due to the amorphous structure of this material type 5013 and 6013 are specified to maintain dimensions, rigidity and tensile strength oven the temperature range -50 to +130 degrees centigrade, whereas the temperature ranges for type 6015 and 6017 are specified to -50 to +150 degrees centigrade and -50 to +170 degrees centigrade respectively. Type 8007 similarly has a specified temperature range of -50 to +70 degrees centigrade. The high rigidity of the above COC material ensures that the centre terminal always remains centred coaxially within the main body of the connector, which is important in order to maintain the correct electrical impedance of the connector. It is furthermore important to maintain correct centring of the centre terminal to insure and facilitate proper connection between the centre terminal 4 and the inner conductor 8 of the cable during mounting of the connector on the cable. Dielectric materials with acceptable mechanical and chemical properties previously used for connectors have suffered from the problem of an unacceptable high dielectric constant, often in the order of 3.7. As mentioned for high frequency applications it is vitally important to keep the dielectric constant as close to unity as possible in order to obtain the highest possible upper limiting frequency of the connector. There exists a number of dielectric materials with relatively low dielectric constants, i.e. dielectric constants in the order 2 to 2.3 but these previously used materials are all very soft and hence not suitable for those dielectric structures in connectors that must be able to withstand large forces during mounting and use of the connectors. Materials such as ABS, Nylon and polycarbonate have dielectric constants in the order 3.1 to 3.7 and are furthermore relatively hard materials, However the thermal properties of these materials are inferiour to COC. Preferably for coaxial connectors for high frequency applications the dielectric constant should be below 3.5 and more preferably below 2.5. The dielectric constant of the above COC material is 2.35. The high degree of dimensional stability makes the above COC material is advantageous during moulding of the support member, as the required tolerances are easy to keep. The above COC material furthermore exhibits a number of advantageous chemical properties. Thus COC is particularly resistant to the effect of isopropanole (which is used for the removal of flooding compound), suds (used as cooling agents during production), hydrochloric acid, sulphuric acid, nitric acid, methanol, ethanol and acetone. Type 6013 of the above COC material is due to its chemical purity and dimensional stability up to 130 degrees centigrade applicable under circumstances where sterilisation using water vapour, hot air, ethyleneoxide gas and gamma- and beta rays must be carried out. Furthermore it is possible to dye COC for instance to fulfil the requirements of particular users. COC exhibits very low water absorption (0,01% at 23 degrees centigrade over 24 hours). Water absorption is a factor of 4 lower than for polycarbonate and approximately a factor 10 lower than for PMMA. COC is furthermore hydrophobic, and changes of humidity in the surroundings do not affect the mechanical properties. Types 5013 and 6013 can furthermore withstand water vapour at temperatures up to 121 degrees centigrade and type 6015 can withstand water vapour at temperatures up to 143 degrees centigrade.

Claims: Use of cyclo-olefin copolymer for dielectric structures in electrical connectors, where said cyclo-olefin copolymer is an amorphous, transparent copolymer based on cyclic and linear olefins according to the formula: Use of cyclo-olefin copolymer according to claim 1, where the dielectric constant is less than 3.5. Use of cyclo-olefin copolymer according to claim 1 or 2, where the dielectric constant is less than 2.5. Use of cyclo-olefin polymer according to any of the preceding claims 1 to 3, where said electrical connectors are coaxial connectors. Use of cyclo-olefin polymer according to claim 4, where said dielectric structures comprise a tubular support member (10), a tubular force transmission member (11) and a tubular bushing (12). Coaxial connector comprising a tubular support member (10), a tubular member (11) for transmission of an axial force and a tubular bushing (12), characterised in that at least one of said tubular support member (10), tubular member (11) for transmission of an axial force and tubular bushing (12) is/are made of dielectric material according to any of the claims 1 to 5.

Inventors: HENNINGSEN JIMMY CIESLA, HENNINGSEN, JIMMY CIESLA
Applicants: CORNING CABELCON AS, CORNING CABELCON A/S
Application year: 2001
Main classification: H01R13
IPC codes: H01R13, H01R9