Flat cable and method of producing it

Abstract

 Flat cable comprising a plurality of conductor units (2a, 2b,...) laterally spaced by intermediate sections, and at least two bonded resin tapes (3a, 3b) holding said conductor units from two opposite directions perpendicu­lar to their lateral spacing. To provide a cable allowing easy separation of individual conductor units, it is proposed that said resin tapes in at least some parts of said intermediate sections between said conductor units are compressed to form at least one longitudinal groove (4) of wedge-shaped cross-section.

Description

[0001] The present invention relates to a flat cable holding a plurality of con­ductors between the resin tapes and integrating them with the bonding or thermal fusible bonding method.

[0002] The flat cable of this kind is thin and has high conductor packing density and is used therefore as the high density transmission path of computers or other electronic apparatuses.

[0003] Since the polytetrafluoroethylene (hereinafter referred to as PTFE) having excellent electrical characteristics and heat resistance property as well as polyimide, these materials cannot be formed by extrusion under the fusing condition. If a flat cable using such dielectric material is produced, a tape is first manufactured and the conductors are held with equal interval between two such tapes. Thereafter, these tapes and conductors are integrated through the bonding or thermal fusible bonding method, disclosed, for example, in the Japanese Patent publication no. 59-41243.

[0004] Since such flat cable according to the prior art is formed thin and has high conductor packing density, it is suitably used in the field of elec­tronic apparatus. But it is easily hardened and is a little difficult to be bent. Moreover, in case the unit conductors are separated individually, the tape may be broken until the adjacent part.

[0005] Therefore, in case the unit conductors are to be separated individually, a sharp blade must be used and even in case the unit conductors are well separated, an insulation fault may easily be generated in individual unit conductors due to delicate clearance between tapes.

[0006] The present invention is therefore intended to provide a tape holding type flat cable for solving problems of the prior art, allowing easy separation of each conductor unit as required and generating no insula­tion fault to each separated unit conductor.

[0007] The present invention therefore provides a flat cable comprising a plura­lity of unit conductors arranged with equal interval and resin tapes holding these unit conductors from both sides and forming a wedge-shaped compressed part to the resin tape between the adjacent unit conductors.

[0008] In such a structure, the wedge-shaped compressed part may be formed in any way as the opposed surfaces of the end part are formed flat, or the end part is formed opposed to each other, or these are mixed.

[0009] According to the present invention, the resin tapes with interposed con­ductors are compressed in the form of a wedge between the unit conduc­tors. Therefore, the tapes are sufficiently integrated, not allowing creeping discharge at the joint. As a result, the dielectric strength at the side end part can be intensified.

[0010] In case the wedge-shaped compressed part is formed with the opposed surfaces of the end part of wedged-shape formed in flat, the unit conduc­tors are not easily separated depending on the direction of force applied. Therefore the tapes still have the sufficient original shape sustaining property but have a remarkably improved flexibility and the unit con­ductors may be separated easily with a force exceeding the specified value or in a certain direction of force applied. Morevover, in case the wedge-shaped compressed part is formed with the end part of wedge-shape formed opposed to each other, unit conductors may be separated easily with a small force and the dielectric strength can also be improved as described earlier.

[0011] The wedge-shaped compressed part with the opposed surfaces of end part of wedge-shape formed in flat and the wedge-shaped compressed part with the opposed surfaces formed opposed to each other are caused to co-exist. For example, these wedge-shaped compressed parts are alter­nately provided in the width direction or in the longitudinal direction of the cable. In such a case, separation may be done easily in the width direction or in the longitudinal direction, but may not be done easily in any other direction.

[0012] Specific embodiments of the invention will be described in detail below with reference to drawings, in which:

Fig. 1 is a partial cross sectional view of a flat cable as an embodiment of the present invention.

Fig. 2 and Fig. 3 are enlarged cross sectional views indicating different embodiments of the wedge-shaped compressed part;

Fig. 4 is a partial cross sectional view of a flat cable as another embodi­ment of the present invention.

[0013] In a flat cable 1 of this embodiment, respective unit conductors 2a 2b, ....., 2n consisting of single bare conductors are arranged with intervals and are held by two sheets of resin tapes 3a, 3b. These resin tapes may be bonded with a bonding agent but are preferably bonded by thermal fusible bonding method in case the PTFE material is used.

[0014] In case the tapes are bonded by the thermal fusible bonding method, the resin tapes 3a, 3b are heated with pressure from both sides. Particularly, in this case the tapes between the unit conductors 2a-2b, 2b-2c, 2c-2d and 2d-2n are compressed with high pressure and thereby the wedge-­shaped compressed parts 4 are formed.

[0015] With formation of such wedge-shaped compressed part 4 through applica­tion of high pressure, both resin tapes 3a, 3b are perfectly integrated. In this case, the joining surface opening externally is closed and thereby the dielectric strength can be improved. In addition, respective unit conductors 2b, 2c, 2d, 2n and resin tapes 3a, 3b are closely integrated without clearance and thereby the conductor strip force can also be improved.

[0016] However, the conductor 2a and resin tapes 3a, 3b are not closely integra­ted forming the clearance 5 at the side end of unit conductor 2a and the joining surface between tapes are opening externally. Therefore, this side end conductor may be used as a grounding conductor or a dummy conductor. But the wedge-shaped compressed part can also be formed to this part.

[0017] As indicated in the embodiment of Fig. 1 and is enlarged in Fig. 2, the wedge-shaped compressed part 4 can be provided by forming a flat sur­face 7 with the opposed surface at the end part of wedge-shape 6.

[0018] In this case, when a force is applied in the upper direction or a force including the upper element is applied to both sides of wedge-shaped com­pressed part 4, crack is easily generated between the end part of wedge-shape 6 and the flat surface 7 and the tape can be separated easi­ly. However, in case a force is to be reversely applied or a force is to be applied in the horizontal direction, a further intensified force is re­quired. Therefore, when the forces in both directions are applied re­peatedly to the part to be separated, for example, by twisting between hands, the tapes can be separated easily but the integrated flat cable may be maintained with the ordinary treatment.

[0019] Meanwhile, as indicated in Fig. 3, in the structure where the wedge-­shaped end parts are provided opposed to each other, the tape may be se­parated easily when a force is applied from any direction. Therefore, in case the wedge-shaped compressed part 4 shown in Fig. 2 and that 4a shown in Fig. 3 where the wedge-shaped end parts 6 are provided opposed to each other coexist, the tape can be separated in the desired part(s) and thereby the cable can be deformed in the three-dimensional shape.

[0020] Another embodiment of the present invention is then explained with reference to Fig. 4.

[0021] In the flat cable 8 of this embodiment, the unit conductors 11a, 11b, 11c are respectively formed by arranging the bare conductors 10a1 - 10a2, 10b1 - 10b2, 10c1 - 10c2 to both sides of the insulated conductors 9a, 9b, 9c with equal intervals. These plural unit conductors 11a, 11b, 11c are respectively held by two sheets of PTFE resin sheets 12a, 12b and these resin sheets are bonded by the thermal fusible bonding method.

[0022] In the thermal fusible bonding process, the wedge-shaped compressed parts 13 are respectively formed between the unit conductors 11a, 11b, 11c.

[0023] The flat cable 8 of this embodiment provides the effect similar to that of flat cable 1 shown in Fig. 1. Since the flexibility of the cable as a whole can be increased, the cable may be rounded or curved in the width direction and easily bent like the character L or in the form of a crank.

[0024] Moreover, this flat cable can be separated respectively into each unit conductor including three conductors.

[0025] As explained earlier, the present invention comprises a plurality of unit conductors arranged with equal intervals and resin tapes holding these unit conductors from both sides. The flat cable having the structure that the wedge-shaped compressed part is formed to the resin tape between the adjacent unit conductors can be separated into respective unit conductors as required. When the unit conductors are separated, each conductor has not only large dielectric strength but also improved flexibility of the cable as a whole. Moreover, the cable may be used by freely bending in the width direction. Namely, the flat cable of the pre­sent invention ensures wide application field through improvement in the degree of freedom on the wiring, in addition to high packing density and good electrical characteristic.

[0026] In case the wedge-shaped compressed part is formed with the opposed surface of wedge-shaped end part formed in flat, the cable may be separated with a force larger than the specified value, but it sustains the original shape under the usual treatment. Furthermore, in case the wedge-­shaped compressed part is formed with the wedge-shaped end part formed opposed to each other, the cable can be separated easily into the unit conductors. Therefore, combination of these structures ensures wide application field of this flat cable.

Claims

1. Flat cable (1, 8) comprising a plurality of conductor units (2a, 2b...; 11a, 11b), laterally spaced by intermediate sections, and at least two bonded resin tapes (3a, 3b; 12a, 12b) holding said conductor units from two opposite directions perpendicular to their lateral spacing, cha­racterized in that said resin tapes (3a, 3b; 12a, 12b) in at least some parts of said intermediate sections between said conductor units (2a, 2b...; 11a, 11b...) are compressed to form at least one longitudinal groove (4, 13) of wedge-shaped cross section.

2. Flat cable according to claim 1, characterized in that said resin tapes (3a, 3b; 12a, 12b) in said intermediate sections have a flat surface (7) on one side, said groove being arranged on the opposing side and the bottom (6) of said groove opposing said flat surface (7).

3. Flat cable according to claim 1, characterized in that said grooves (4) are arranged on both sides of said intermediate sections, said bottoms (6) of said grooves opposing each other.

4. Flat cable according to claim 1, characterized in that said inter­mediate sections comprise regions having grooves (4) opposing each other and other regions in which grooves (4) on one side oppose a flat surface (7) on the other side.

5. Flat cable according to anyone of claims 1-4, characterized in that said grooves (4; 13) are V-shaped with a tip-like bottom (6) in cross section.

6. Flat cable according to anyone of claims 1-5, characterized in that said resin tapes are made of polytetrafluorethylene and integrated with each other through thermal fusible bonding.

7. Method of producing a flat cable (1) comprising the steps of arranging conductor units (2a, 2b,...; 11a, 11b...) in laterally spaced re­lation, covering said conductor units from both sides perpendicular to their lateral spacing by at least two resin tapes (3a, 3b; 12a, 12b) and integrating said resin tapes through a thermal fusible bonding method, characterized in that simultaneously to the integration of said resin tapes (3a, 3b; 12a, 12b) these are compressed to form at least one longi­tudinal groove (4, 13) of wedge-shaped cross-section in sections of said resin tapes lying between said conductor units (2a, 2b,...; 11a, 11b,...).

Drawing