Flat cable and process for producing the same

Details Flat cable and process for producing the same Flat cable and process for producing the same

1999-07-14

2002-05-21

Reichard, Dean A. (Department: 2831)

Electricity: conductors and insulators

Conduits, cables or conductors

Insulated

C029S825000

Reexamination Certificate

active

06392155

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to a flat cable and a process for producing the same, and more particularly to a flat cable, which can eliminate the need to increase the width dimension without detriment to electric characteristics and further has a stable structure, and a process for producing the same.
BACKGROUND OF THE INVENTION
A flat cable generally comprises: linear portions each comprising a plurality of insulated conductors juxtaposed to one another, the insulated conductors each comprising a conductor covered with an insulative layer; and twisted pair portions provided alternately with the linear portions, the twisted pair portions each comprising a plurality of twisted pairs juxtaposed to each other or one another, the twisted pairs each being composed of two insulated conductors which extend from the linear portions and are twisted together.
In flat cables of this type, the construction of the linear portion is an important element. Improper construction of this portion, for example, adversely affects the connection of conductors of the insulated conductors in the linear portion to a connector, making it impossible for the flat cable to have contemplated functions.
In a first conventional flat cable, the linear portion has such a construction that a plurality of insulated conductors each comprising a conductor covered with an insulative layer are provided side by side while leaving a spacing between adjacent insulated conductors, and the plurality of insulated conductors are sandwiched between upper and lower resin tapes in such a manner that the upper and lower resin tapes are fused to each other in a portion between adjacent insulated conductors.
In a second conventional flat cable, the linear portion comprises: a plurality of insulated conductors with adjacent insulated conductors in their insulative layers being fused to each other to constitute an integral insulative layer having crest portions and root portions; and a resin tape which is provided on one surface of the integral insulative layer so that it is spottily adhered to the integral insulative layer in its crest portions.
Flat cables having the above constructions, wherein the linear portions have been flattened by the resin tape, have been extensively used for internal wiring in electronic equipment, such as personal computers.
The conventional flat cables having the above constructions, however, have the following drawbacks. In the linear portions of the first conventional flat cable, the resin tape is provided between adjacent insulated conductors. This results in increased width dimension of the flat cable. In the case of flat cables, in many cases, the width dimension is regulated. The construction of the first conventional flat cable in its linear portions makes it difficult to follow the regulation value. Reducing the diameter of the insulated conductors is considered effective for overcoming this difficulty. This, however, leads to deteriorated electric characteristics of the flat cable. Further, regarding the dimensional accuracy, in the linear portions of the first conventional flat cable, the accuracy of the pitch between insulated conductors is low due to the presence of the resin tape between adjacent insulated conductors. This is likely to cause a failure of fitting at the time of pressure contact connection.
On the other hand, according to the construction of the linear portions in the second flat cable, there is no need to widen the portion between adjacent insulated conductors, and the accuracy of pitch between insulated conductors is high. In the linear portions of the second conventional flat cable, however, since the resin tape is spottily adhered to the insulative layer, there is a fear of the resin tape being separated from the insulative layer. Further, this construction has an additional problem that, at the time of simultaneous connection of conductors of the insulated conductors to a connector, it is difficult to insert pins of the connector, leading to poor fitting between the cable and the connector.
Next, a general conventional production process of flat cables will be explained. A predetermined number of insulated conductor pairs are first provided. Each of the insulated conductor pair is composed of two insulated conductors each comprising a conductor covered with an insulative layer, and has linear portions and twisted pair portions provided alternately with the linear portions at predetermined spacing. In the linear portions, the two insulated conductors are juxtaposed to each other, while in the twisted pair portions, the two insulated conductors are twisted together. The predetermined number of insulated conductor pairs are placed side by side and, in this state, are fed from a bobbin (not shown) into a mold. The mold is split into two parts, openable upper mold and lower mold. The upper and lower molds have grooves the number of which is such as will be able to receive all the insulated conductors in the linear portions. In the grooves, the insulated conductors are placed in such a positional relationship that adjacent conductors come into contact with each other. In this state, upon application of heat from the mold, the adjacent insulated conductors in their insulative layers are fused to each other to form a belt comprising insulated conductors connected to one another, thereby providing a linear portion wherein the surface of the integrated insulative layer has crest portions and root portions as viewed in the cross section of the linear portion.
The fusion of the insulated conductors to one another is carried out on a batch basis rather than a continuous basis. After the formation of the linear portion, the mold is opened. In this state, the twisted portion is passed through the mold. A next linear portion is then fed into the mold, and fusion of the insulated conductors to one another is again carried out. The above procedure is then repeated.
After the insulated conductor pairs in their linear portion are integrated with one another in the mold, they emerge from the mold, are passed through a take-up unit, and, together with a resin tape, are fed into between heating rollers to fuse the resin tape to one surface thereof. Thus, a predetermined flat cable is obtained wherein, in the linear portions, the resin tape has been spottily adhered onto the integral insulative layer in its crest portions.
The flat cable, of which the flatness of the linear portions is kept by the resin tape, enables simultaneous connection of conductors in the linear portion to a connector and hence has been extensively used in various types of electronic equipment including personal computers, and a further increase in demand thereof is expected.
In the conventional process of a flat cable, the adhesion of the resin tape to the integral insulative layer is intermittent. That is, the resin tape is adhered to only the crest portions of the integral insulative layer. This leads to a fear of the resin tape being separated from the insulative layer. This further poses a problem that, at the time of simultaneous connection of conductors in the linear portion to a connector, the resin tape in its portion floating above the root portions of the integral insulative layer inhibits fitting between the linear portion and the connector. The above problems are attributable to fusion using heating rollers, and hence are unavoidable without the elimination of reliance of the fusion upon the heating rollers.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the invention to provide a flat cable that can eliminate the need to increase the width dimension without detriment to electric characteristics, has high accuracy of pitch between insulated conductors, and has a stable structure having no fear of the resin tape being separated from the insulative layer.
It is another aspect of the invention to provide a process for producing a flat cable that enables the resin tape to be fused to the resin layer so as to conform to the shape of the surface of the insulative layer without spot fusi

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