JPH0628925A - Flat cable - Google Patents

Abstract

PURPOSE:To enhance fatigue resistance of a flat cable so as to improve reliability of equipment using this kind of flat cable by setting a surface roughness of a tape-like conductor to 0.2-1.5mum. CONSTITUTION:In a flat cable provided with an insulating film 2 bonded onto both sides of a tape-like conductor 1 made of plural strips of copper or copper alloy, a surface (Ra) of the conductor 1 is set to 0.2-1.5mum. Otherwise, plating is applied to the surface of the conductor 1, where a surface roughness (Ra) of the plating is set to 0.2-2.5mum. The conductor 1 having the above-stated surface roughness is manufactured by the following methods and the like: (1) The conductor is rolled by means of a roller, to which surface a dull processing is applied by liquid honing, laser machining, mechanical polishing, or the like. (2) The surface of the conductor 1, which is rolled by means of an ordinary roller is dissolved chemically. (3) Plating is applied to the surface of the conductor 1. Consequently, it is possible to remarkably enhance fatigue resistance of the flat cable.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flat cable used under the condition of being repeatedly bent.

[0002]

2. Description of the Related Art For example, a steering shaft of an automobile includes a vehicle body (fixed body) side and a steering wheel (reciprocating rotary body).
In order to exchange electric signals with the side, a flat cable wound with a spiral spring is used. In this flat cable, the inner end side of the mainspring winding is on the steering shaft side,
The outer end side is connected to the vehicle body side, and when the steering wheel rotates, the winding of the mainspring is tightened or loosened, so that the fixed body and the reciprocating rotary body are connected without a sliding contact portion.

Further, in printers and the like, a flat cable is used for exchanging electric signals between the device body (fixed body) side and the head (reciprocating body) side. In this case, the flat cable is turned in the middle, and one end of the flat cable is connected to the device body side and the other end is connected to the head side to enable the head to reciprocate.

A flat cable connecting such a fixed body and a reciprocating rotary body or a reciprocating movable body is repeatedly bent in a state of use, and therefore must be sufficiently durable. Particularly, in an automobile or the like having an airbag mounted on the steering wheel, if the flat cable is repeatedly bent and the conductor breaks due to fatigue, the airbag may not operate and a life-threatening problem may occur.

A conventional flat cable of this type is shown in FIG.
As shown in FIG. 3, a plurality of tape-shaped conductors 1 arranged in parallel are sandwiched by insulating films 2 from both sides and bonded. The tape-shaped conductor 1 is made of copper or a copper alloy, and the insulating film 2 is made of a polyester film or the like. As the adhesive 3 (see FIG. 3) for adhering these, a heat-crosslinking adhesive or the like is used. Depending on the application, a flat cable with one tape-shaped conductor may be considered.

[0006]

In order to improve the fatigue resistance of such a flat cable, conventionally, the fatigue resistance of the constituent members such as the tape-shaped conductor, the insulating film and the heat-crosslinkable adhesive can be improved. Has been considered. For example, in the case of a tape-shaped conductor, it has been studied to improve the fatigue resistance of the conductor by adding an alloy element. Further, in the case of insulating films and adhesives, it has been studied to improve the fatigue resistance by changing the material and for the thermally crosslinkable adhesive, changing the degree of crosslinking.

However, the addition of an alloying element to improve the fatigue resistance of the tape-shaped conductor has a drawback that it causes an increase in conductor resistance and limits its use, and that the materials for the insulating film and the adhesive are changed. Has the problem of increasing costs.

[0008]

Means for Solving the Problem and Its Action As a result of intensive investigations by the present inventors in view of the above problems, it was found that the fatigue resistance of a flat cable correlates with the surface roughness of a tape-shaped conductor. I found it. That is, the conventional flat cable uses a tape-shaped conductor made of copper or a copper alloy rolled by an ordinary rolling roll, and its surface roughness (Ra) is about 0.1 μm. It was experimentally confirmed that if the surface roughness (Ra) is made slightly rougher than that, the fatigue resistance of the flat cable is dramatically improved.

The present invention has been made on the basis of such knowledge, and its constitution is a flat cable in which insulating films are adhered to both surfaces of a tape-shaped conductor made of one or a plurality of copper or copper alloys. The tape-shaped conductor has a surface roughness (Ra) of 0.2 to 1.5 μm. The reason why the surface roughness of the tape-shaped conductor is set to the above range is that the effect of improving fatigue resistance is not sufficient if it is less than 0.2 μm, and if it exceeds 1.5 μm, conversely stress concentration occurs on uneven parts and fatigue resistance is reduced. This is because it will decrease.

The tape-shaped conductor is made of copper or a copper alloy, but the surface may be plated with another metal or the same metal. In the case of a tape-shaped conductor with a plated surface, it was confirmed that the fatigue resistance was improved when the plated surface roughness was in the range of 0.2 to 2.5 μm. This is because, unlike the case of rolling, the plated surface does not have mechanically formed unevenness, so the shape is different and stress concentration is less likely to occur, and fatigue resistance is less likely to deteriorate.

As means for producing the tape-shaped conductor having the above-mentioned surface roughness, a method of rolling the conductor with a rolling roll subjected to surface dull processing such as liquid honing processing, laser processing or mechanical polishing, or ordinary rolling is used. Effective methods include chemically dissolving the surface of the tape-shaped conductor rolled with a roll, and plating the surface of the tape-shaped conductor rolled with a normal rolling roll with copper, tin, tin-lead alloy or nickel. Was confirmed. Among the above-mentioned means, the more effective method is to improve the fatigue resistance of the flat cable.

[0012]

EXAMPLES Next, examples of the present invention will be described in detail. In the final rolling process of the tape-shaped conductor, final rolling is performed using various rolling rolls that have been subjected to surface honing processing by laser honing, laser processing, or mechanical polishing, and four types of tape-shaped conductors with different surface roughness. Was manufactured. The thickness of the tape-shaped conductor is 0.10 mm, and the material is tough pitch copper. The measurement results of the surface roughness (Ra) of the tape-shaped conductor were 0.10 μm, 0.55 μm, 1.38 μm and 1.55 μm (Sample Nos. 1 to 4). A plurality of tape-shaped conductors were arranged in parallel, and a polyester film was bonded to both surfaces of the tape-shaped conductor with a heat-crosslinking adhesive to manufacture a flat cable having a thickness of 0.25 mm.

The surface of the tough pitch copper tape was dissolved with sulfuric acid or nitric acid, and the melting conditions at that time were changed to manufacture four types of tape-shaped conductors (thickness 0.10 mm) having different surface roughnesses. The measurement result of the surface roughness (Ra) of the tape-shaped conductor is 0.
15 μm, 0.66 μm, 1.29 μm, 1.75 μm (Sample N
o. 5-8). A plurality of tape-shaped conductors were arranged in parallel, and a polyester film was bonded to both surfaces of the tape-shaped conductor with a heat-crosslinking adhesive to manufacture a flat cable having a thickness of 0.25 mm.

2μ thick on the surface of tough pitch copper tape
Apply m tin plating and change the plating conditions at that time,
5 types of tape-shaped conductors with different surface roughness (thickness 0.10mm)
Was manufactured. The measurement results of the surface roughness (Ra) of the tape-shaped conductor are 0.13 μm, 0.57 μm, 1.55 μm, 2.15 μm, 3.11
μm (Sample Nos. 9 to 13). A plurality of tape-shaped conductors were arranged in parallel, and a polyester film was bonded to both surfaces of the tape-shaped conductor with a heat-crosslinking adhesive to manufacture a flat cable having a thickness of 0.25 mm.

In each of the above examples, the surface roughness (Ra) of the tape-shaped conductor complies with the definition and measurement method defined in JIS B-0601 and is as follows. Ra: It is called center line average roughness, and a portion of the measurement length L is extracted from the roughness curve in the direction of the center line, the center line of this extracted portion is the X axis, and the direction of longitudinal magnification is the Y axis. When a curve is represented by y = f (x), it means that the value obtained by the following formula is represented in micrometers (μm).

[0016]

[Equation 1]

The flat cable manufactured as described above is set in a repeated bending tester as shown in FIG.
The number of times until the tape-shaped conductor was broken was measured in a state where a current was applied to the tape-shaped conductor of the flat cable 4 from a power source (not shown). In FIG. 4, 5 is a clamp that fixes the base of the flat cable 4, 6 is a vibrating head that vibrates the free end side of the flat cable 4, S is the set length of the flat cable 4, and H is the amplitude of the vibrating head 6. . The test conditions are set length S = 9 mm, swing width H / 2 =
2 mm, vibration frequency = 50 Hz, the number of times counted is one vibration cycle. The above test results are shown in Table 1.

[0018]

[Table 1]

As is clear from Table 1, a flat cable whose surface roughness of the tape-shaped conductor falls within the range of the present invention has fatigue resistance characteristics (the conductor breaks due to repeated bending) more than flat cables outside the range of the present invention. It can be seen that the number of times up to) is significantly superior. Further, it can be seen that when the surface treatment method of the tape-shaped conductor is plating, the fatigue resistance is not deteriorated even if the surface roughness is slightly rougher than other methods.

[0020]

As described above, according to the present invention, it is possible to greatly improve the fatigue resistance of a flat cable that is repeatedly bent during use, and to improve the reliability of equipment using this type of flat cable. There is a remarkable effect that it can greatly contribute to the improvement.

[Brief description of drawings]

FIG. 1 is a plan view showing an example of a flat cable.

FIG. 2 is a sectional view of the flat cable of FIG. 1 taken along the line AA.

FIG. 3 is an enlarged cross-sectional view of portion B in FIG.

FIG. 4 is an explanatory diagram of a repeated bending tester for flat cables.

[Explanation of symbols]

 1: Tape-shaped conductor 2: Insulating film 3: Thermal crosslinking adhesive

Claims (2)

[Claims] 1. A flat cable in which an insulating film is adhered to both surfaces of a tape-shaped conductor made of one or more strips of copper or copper alloy, and the surface roughness (Ra) of the tape-shaped conductor is 0.2 to 1.5. A flat cable characterized by having a size of μm. 2. A flat cable in which an insulating film is adhered to both sides of a tape-shaped conductor made of one or more strips of copper or copper alloy, and the tape-shaped conductor is plated on its surface. Surface roughness (Ra) of
A flat cable characterized by having a thickness of 0.2 to 2.5 μm.