Tubular circuit connector

Abstract: Disclosed is a rubber-based tubular circuit connector comprising; (A) an elongated tubular body of an electrically insulating rubber as a core tube; and (B1) a multiplicity of ring-formed contacting layers of a metal formed on an d around the core tube as arranged in the axial direction of the core tube at a regular pitch, each of the ring-formed contacting layers being electrically insulated from the adjacent cladding layer with intervention of (B2) a ring-formed coating layer of a polysilane compound on and around the surface of the core tube. The rubber-based tubular connector is prepared by (a) forming a coating layer of a polysilane compound on the whole outer surface of an elongated tubular body of an electrically insulating rubber; (b) irradiating the coating layer of a polysilane compound with ultraviolet light on a multiplicity of ring-formed areas arranged at a regular pitch in such a dose that the polysilane compound is converted into silica; and (c) forming a multiplicity of ring-formed plating layers of gold to serve as the contacting layer on the ultraviolet-irradiated ring-formed areas of the tubular body.

Description: BACKGROUND OF THE INVENTION The present invention relates to a tubular circuit connector or, more particularly, to a rubber-based tubular circuit connector used for electric connection of circuits, for example, between a liquid crystal display unit and a circuit board for driving the same, between two display units or between two circuit boards as well as to a unique method for the preparation thereof. As is well known, a variety of modem electric and electronic instruments are manufactured by assembling a plurality of working units, e.g., liquid crystal display modules, and circuit boards to provide an electric circuit for driving the working unit. The electric connection between the electrode terminals of the working units and the circuit boards is established by using an electric circuit connector, referred to simply as a connector hereinafter. While various types of connectors are known and employed in the prior art, the most widely employed connector is a rubber-based connector of which the reliability of electric contacting between electrode terminals is ensured by utilizing the elastic resilience of a rubber-made member. For example, the so-called "zebra"-type rubber-based connector is an integral elongated body having a stratified structure consisting of a lengthwise alternate stratification of a multiplicity of layers of an electrically insulating rubber and a multiplicity of layers of an electroconductive rubber, which is a composite rubber compounded with an electroconductive powder such as a conductive carbon black and silver powder, to exhibit a black-and-white striped appearance. It is usual in the above described "zebra" connectors that the composite rubber forming the conductive layers has a relatively high volume resistivity so that the connectors of this type are not quite satisfactory for electric connection between electrode terminals where a low electric resistance is essential as in the connection of color liquid crystal display modules and monochrome liquid crystal display modules of 18 or more gradations because of the possible variation in the performance of the liquid crystal display as being affected by the contact resistance unless the contact resistant is controlled to be negligibly small. The "zebra" connectors are also not suitable for electric connection when the electric current passing each of the conductive layers is large to exceed, for example, 10 mA as in the connection of plasma display modules because of the temperature elevation due to the heat generated therein as a consequence of the high resistance. Furthermore, the rubber layers constituting the "zebra" connectors have a relatively high rubber hardness so that reliable electric connection can hardly be obtained between the electrode terminal and the conductive layer of the connector unless the contacting pressure therebetween is unduly increased to such an extent that the circuit board for connection is under a risk of warping or distortion by the large contacting pressure which may lead to a decrease in the stability of electric connection with the connector. This problem of course can be solved by increasing the thickness of the substrate board of the circuit board to withstand the large contacting pressure. This means, howqever, can not always be employed because an increased thickness of the circuit board requires on the other hand a decrease in the thickness of the working unit such as the liquid crystal display modules, for example, in mobile telephones which must be very compact in volume and light in weight. When the electroconductive rubber forming the conductive layers of the "zebra" connector is a composite rubber compounded with silver particles, in addition, the phenomenon of electromigration of silver atoms sometimes takes place between the electrodes to cause deposition of silver metal on the electrode surface resulting in a decrease in the reliability of electric connection through the connector. Document DE-A-3 008 110 discloses a connector according to the preamble of claim 1. SUMMARY OF THE INVENTION The present invention accordingly has an object to provide an improved rubber-based circuit connector free from the above described problems and disadvantages in the prior art rubber-based circuit connectors or, in particular, the "zebra" connectors and capable of electrically connecting oppositely positioned arrays of electrode terminals with relatively low resistance and with high reliability and stability. Thus, the rubber-based circuit connector provided by the present invention is basically an integral tubular body consisting of an elongated tubular body of an electrically insulating rubber as a core tube and a multiplicity of electrically conductive ring-formed areas formed at a regular pitch on and around the core tube as arranged in the axial direction, the adjacent conductive ring-formed areas being insulated each from the other by intervention of a ring-formed insulating area. According to the invention, the inventive tubular circuit connector comprises: (A) an elongated tubular body of an electrically insulating rubbery material as a core tube; and (B1) a multiplicity of ring-formed contacting layers of a metal formed on and around the core tube as arranged in the axial direction of the core tube at a regular pitch, each of ring-formed contacting layers being electrically insulated from the adjacent cladding layer with intervention of (B2) a ring-formed coating layer of a polysilane compound on and around the surface of the core tube. Though optional, it is advantageous that a pair of elongated reinforcement rubber strips are adhesively bonded to the cladding layers along the radially opposite axial lines so as to improve reliability in handling. The above described rubber-based connector according to the first aspect of the invention can be prepared, for example, by a method according to the invention which comprises the steps of: (a) forming a coating layer of a polysilane compound on the whole outer surface of an elongated tubular body of an electrically insulating rubber; (b) irradiating the coating layer of a polysilane compound with ultraviolet light on a multiplicity of ring-formed areas arranged at a regular pitch in such a dose that the polysilane compound is converted into silica; and (c) forming a multiplicity of ring-formed plating layers of gold to serve as the contacting layer on the ultraviolet-irradiated ring-formed areas of the tubular body. BRIEF DESCRIPTION OF THE DRAWING Figures A to F are each a schematic illustration of the steps for the preparation of the inventive rubber-based tubular connector each by a perspective view of the workpiece according to the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS According to the invention, of which the steps for the preparation of the tubular connector 4 are illustrated in Figures A to F, the core tube 1 (Figure A) of an electrically insulating rubbery material is supported on a mandrel 10 and first coated with a polysilane compound to form a uniform coating layer 20 over the whole outer surface of the core tube 1. A polysilane compound is a kind of organosilicon polymers having good solubility in various organic solvents and exhibiting excellent resistance against oxygen plasma and stability. In particular, polysilane compounds are suitable for pattering by pattern-wise irradiation with ultraviolet light. Among the various types of polysilane compounds, polyphenylsilanes having a linear molecular structure are preferred in the invention. The coating layer 20 formed from a polysilane compound should have a thickness in the range from 0.1 to 20 µm as dried. When the thickness of the polysilane layer 20 is too large, the layer 20 is imparted with increased rigidity resulting in a decrease in the compatibility with deformation of the core tube 1, The layer 20 of a polysilane compound can be formed by coating the surface of the core tube 1 with a solution of the polysilane compound in an organic solvent followed by drying. The next step to follow formation of the polysilane layer 20 over the whole outer surface of the core tube 1 (Figure 1B) is selective ultraviolet irradiation of the polysilane layer 20 pattem-wise in the ring-formed areas around the core tube 1. Since a polysilane compound can be decomposed by irradiation with ultraviolet light in an oxidizing atmosphere into silica, this step of selective irradiation of the polysilane layer 20 can be performed by irradiating the layer with ultraviolet light W through a masking sheet 15 having a plurality of slits 15A, which may be straightly linear or wavy as in Figures C, arranged at a desired pitch white the core tube 1 is rotated around the axis by means of the mandrel 10 inserted into the core tube 1 so that the polysilane compound is converted into silica forming a plurality of ring-formed layers 20A of silica around the core tube 1 each between two ring-formed polysilane layers 20 (Figure D). The contacting layers 30 of gold are formed on the ring-formed areas where the polysilane has been converted into silica layers 20A by a suitable method after removal of the silica (Figure E). Finally, though optional, the thus obtained tubular connector 40 is provided on one or both sides each with a reinforcement rubber strip or strips 7 adhesively bonded thereto (Figure F) before removal of the mandrel 10. In the following, the rubber-based tubular circuit connector and the method for the preparation thereof according to the present invention are described in more detail by way of Examples. Example 1. A silicone rubber compound (KE 151 U, a product by Shin-Etsu Chemical Co.) was kneaded and compounded with a curing agent on a mixing roller to be plasticized and the thus plasticized silicone rubber composition was extrusion-molded into a continuous-length tube having an outer diameter of 3.4 mm and an inner diameter of 2.0 mm, which was subjected to a curing treatment by heating in a hot-air oven at 1995°C for 3 minutes. The thus cured continuous-length silicone rubber tube was divided by cutting into unit-length tubes 1 each having a length of 300 mm. A stainless steel mandrel 10 having a length of 400 mm and a diameter of 2.1 mm was inserted into the bore of the 300 mm-long tubular body 1 which was mounted on a printing machine by the mandrel 10 and coated thereon with a plastic resin-containing coating composition by rotating around the axis and moving in the axial direction followed by drying to form a uniform coating layer 2 of the plastic resin having a thickness of 10 µm. In the next place, the plastic resin layer as the base layer 2 was removed selectively in ring-formed areas by means of a YAG laser beam of 50 µm spot diameter to form ring grooves 5 each having a width of 50 µm and a depth of 20 µm at a regular pitch of 0.1 mm arranged along the axial direction of the core tube 1, where the underlying rubber layer of the core tube 1 was exposed bare. The YAG laser was operated at an output of 600 watts and the working time was 0.5 second for each of the ring grooves 5. Theplastic resin layer 2 divided into ring areas of each 50 µm width as separated with intervention of a ring groove 5 of 50 µm width were each dually plated first with nickel in a thickness of 1 µm and then with gold in a thickness of 0.5 µm to serve as the contacting layer 3. Separately, strips of an uncured silicone rubber composition having a width of 1 mm and a thickness of 0.1 mm were prepared from the same silicone rubber compound (KE 151 U, supra ) and they were attached to the radially opposite side surfaces of the core tube 1 followed by a heat treatment at 185°C for 30 minutes to effect curing of the silicone rubber composition into a cured silicone rubber having a high rubber hardness of 80°H in the JIS A scale to serve as the reinforcement rubber strips 7,7. Finally, the stainless steel mandrel 10 was removed from the tubular body 4 which was then divided by cutting along the axial direction into unit-length pieces each having a length of 10 mm to serve as a circuit connector according to the present invention. Example 2. A continuous-length tube of an uncured silicone rubber composition having an outer diameter of 3.0 mm and an inner diameter of 2.0 mm was prepared from a silicone rubber compound (KE 151U 100, a product by Shin-Etsu Chemical Co.) in about the same manner as in Example 1 and subjected to a curing treatment by heating in a hot-air oven at 195°C for 3 minutes to give a continuous-length tubular body of a cured silicone rubber. The continuous-length tube was divided into unit-length tubular bodies each having a length of 300 mm. The 300 mm-long core tube 1 supported by a 400 mm long stainless steel mandrel 10 of 2.1 mm diameter inserted into the bore of the core tube 1 was set in the vacuum chamber of a sputtering apparatus and a sputtered coating layer of conductive indium oxide having a thickness of 30 nm to serve as the base layer 2 was formed on the whole outer surface of the core tube 1 under rotation around the mandrel 10 and moving in the axial direction taking 1000 seconds. The subsequent procedure for the preparation of the tubular circuit connectors of the invention was substantially the same as in Example 1 including the steps of formation of ring grooves 5 having the same dimensions and arranged at the same pitch as in Example 1 to serve as the base layers 2, formation of the dual plating layer of nickel and gold thereon, each plating layer having the same thickness as in Example 1, and bonding of two reinforcement rubber strips 7,7 onto the radially opposite outer surfaces of the tubular body 4 followed by dividing the same into 10 mm-long pieces. Example 3. A continuous-length tube of an uncured silicone rubber composition having an outer diameter of 3.4 mm and an inner diameter of 2.0 mm was prepared from the same silicone rubber compound as used in Example 1 and subjected to a curing treatment by heating in a hot-air oven at 195°C for 3 minutes. The continuous-length cured silicone rubber tube was divided by cutting into unit-length tubes each having a length of 300 mm. A 400 mm long stainless steel mandrel 10 of 2.1 mm diameter was inserted into the bore of the 300 mm-long tubular body as the core tube 1 and the whole outer surface of the core tube 1 was uniformly coated with a coating composition of a polyphenylsilane having a straightly linear molecular structure followed by drying at 120°C for 10 minutes to form a coating layer 20 of the polyphenylsilane. The coating layer 20 of the polyphenylsilane was then irradiated with ultraviolet light of 254 nm wavelength emitted from a low-pressure mercury lamp on the ring-formed areas by rotating the core tube 1 around the mandrel 10 under a masking sheet 15 having slits 15A of 0.05 mm width at a regular pitch of 0.1 mm as is illustrated in Figure 5C taking 10 minutes so that the polyphenylsilane in the irradiated areas was decomposed and converted into silica forming the ring-formed silica layers 20A each of which had a width of 0.05 mm in the form of a wavy ring keeping parallelism with the other ring-formed silica layers 20A. The tubular body 1 on which a plurality of ring-formed silica layers 20A were formed in the above described manner was dipped in a solution of a noble metal salt to deposit colloidal particles of the noble metal on the silica layers 20A. Thereafter, the tubular body was subjected to an electroless plating treatment to form a plating layer of nickel having a thickness of 1 µm on the surface of the silica layers 20A bearing the colloidal particles of the noble metal. A plating layer of gold having a thickness of 0.5 µm was then formed on the nickel plating layer to serve as the contacting layer 30. The subsequent procedure for the preparation of the inventive tubular circuit connectors of unit length was substantially the same as in Example 1 including the steps of bonding reinforcement rubber strips 7,7 onto the radially opposite side surfaces of the tubular body, removal of the stainless steel mandrel 10 from the tubular body and dividing the 300 mm-long tubular body 40 into 10 mm-long individual unit-length connector pierces.

Claims: A rubber-based tubular circuit connector which is an integral tubular body comprising: (A) an elongated tubular body of an electrically insulating rubber as a core tube; and (Bl) a multiplicity of ring-formed contacting layers (30) of a metal formed on and around the core tube as arranged in the axial direction of the core tube at a regular pitch, each of the ring-formed contacting layers being electrically insulated from the adjacent cladding layer characterised in that this insulation is performed with intervention of a ring-formed coating layer (20) of a polysilane compound on and around the surface of the core tube. A method for the preparation of the rubber-based tubular circuit connector as defined in claim 1 which comprises the steps of: (a) forming a coating layer of a polysilane compound on the whole outer surface of an elongated tubular body of an electrically insulating rubber; (b) irradiating the coating layer of a polysilane compound with ultraviolet light on a multiplicity of ring-formed areas arranged at a regular pitch in such a dose that the polysilane compound is converted into silica; and (c) forming a multiplicity of ring-formed plating layers of gold to serve as the contacting layer on the ultraviolet-irradiated ring-formed areas of the tubular body. An electronic instrument assembled by comprising two sets of electrode terminals arranged in oppositely facing first and second arrays in which the electrode terminals of the first array and the electrode terminals of the second arrays are electrically connected with intervention of the rubber-based tubular circuit connector as defined in claim 1 therebetween under a compressive force to deform the tubular body of rubber with elastic resilience.

Inventors: MATSUMOTO SHUZO, MATSUMOTO, SHUZO
Applicants: SHINETSU POLYMER CO, SHIN-ETSU POLYMER CO., LTD.
Application year: 2000
Main classification: H01R13
IPC codes: H01R43, H01R13