U.S. patent application number 10/046271 was filed with the patent office on 2003-01-30 for bending-resistant flexible flat cable and production process thereof.
This patent application is currently assigned to HITACHI CABLE, LTD.. Invention is credited to Aoyama, Seigi, Endo, Katsuo, Ichikawa, Takaaki, Ito, Masato, Kobayashi, Hidenori, Komori, Tsutomu, Yamanobe, Hiroshi.
Application Number | 20030019659 10/046271 |
Document ID | / |
Family ID | 19050156 |
Filed Date | 2003-01-30 |
United States Patent
Application |
20030019659 |
Kind Code |
A1 |
Yamanobe, Hiroshi ; et
al. |
January 30, 2003 |
BENDING-RESISTANT FLEXIBLE FLAT CABLE AND PRODUCTION PROCESS
THEREOF
Abstract
In FFCl integrated by sandwiching flat type conductors 2 between
plastic films 3 with adhesives, wherein the conductors are formed
of pure copper or a copper alloy having a wiredrawing draught of at
least 95% and an elongation of at least 5%, and the plastic films
with adhesives are formed of one having a modulus of longitudinal
elasticity of at least 280 kg/mm.sup.2 and an elongation of at
least 80%, and the 180.degree. peel strength between the adhesives
and the conductors 2 is made to be at least 0.8 kg/cm. As a result,
even if the number of conductors 2 is increased than the
conventional FFC, bending-resistant characteristic equal to or
higher than the conventional FFC can be exhibited.
Inventors: |
Yamanobe, Hiroshi; (Ibaraki,
JP) ; Ichikawa, Takaaki; (Ibaraki, JP) ;
Aoyama, Seigi; (Ibaraki, JP) ; Komori, Tsutomu;
(Ibaraki, JP) ; Kobayashi, Hidenori; (Ibaraki,
JP) ; Ito, Masato; (Ibaraki, JP) ; Endo,
Katsuo; (Ibaraki, JP) |
Correspondence
Address: |
FOLEY AND LARDNER
SUITE 500
3000 K STREET NW
WASHINGTON
DC
20007
US
|
Assignee: |
HITACHI CABLE, LTD.
|
Family ID: |
19050156 |
Appl. No.: |
10/046271 |
Filed: |
January 16, 2002 |
Current U.S.
Class: |
174/117FF |
Current CPC
Class: |
H05K 3/386 20130101;
H05K 1/028 20130101; H05K 3/281 20130101; H01B 7/0838 20130101;
H05K 3/202 20130101; H05K 1/09 20130101 |
Class at
Publication: |
174/117.0FF |
International
Class: |
H01B 007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 16, 2001 |
JP |
2001-215534 |
Claims
What is claimed is:
1. A bending-resistant flexible flat cable integrated by
sandwiching a single or a plurality of flat type conductors between
plastic films with adhesives, wherein said conductor is formed of
pure copper having a wiredrawing draught of at least 95% and an
elongation of at least 5%, or a solution-type high-conductivity
copper alloy having a conductivity of at least 70%, said plastic
film with adhesives is formed of one having a modulus of
longitudinal elasticity of at least 280 kg/mm.sup.2 and an
elongation of at least 80%, and the 180.degree. peel strength
between the adhesives of the plastic film with adhesives and the
conductor is made to be at least 0.8 kg/cm.
2. A bending-resistant flexible flat cable according to claim 1,
wherein said solution-type high-conductivity copper alloy is a
copper alloy in which at least one kind of Sn or In is added in Cu
in an amount of from 0.05 to 0.5% in total.
3. A bending-resistant flexible flat cable according to either one
of claim 1 and claim 2, wherein said plastic film with adhesives is
polyethylene terephthalate, polyethylene naphthalate, polyphenylene
sulfide or polyetherimide, with flame retardant polyester type
adhesives.
4. A bending-resistant flexible flat cable according to any one of
claim 1 to claim 3, wherein the adhesives of said plastic film with
adhesives contains a thermoplastic component, a thermal
crosslinking component and a flame retardant component.
5. A production process of a bending-resistant flexible flat cable
comprising steps of: forming a flat type conductor having a
wiredrawing draught of at least 95% and elongation of at least 5%
from pure copper or a solution-type high-conductivity copper alloy
having a conductivity of at least 70%; sandwiching a single flat
type conductor or a conductor group having a plurality of flat type
conductors arranged parallel with each other between nonconductive
plastic films with adhesives having a modulus of longitudinal
elasticity of at least 280 kg/mm.sup.2 and an elongation of at
least 80%, using hot rolls from the upper and lower sides thereof;
and heating and curing the adhesives.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a bending-resistant
flexible flat cable (hereinafter referred to as FFC) widely used as
a wiring material for movable parts in circuits of electric and
electronic equipments, and the production process thereof.
[0003] 2. Prior Art
[0004] The FFC heretofore widely used as a wiring material for
movable parts in circuits of electric and electronic equipments is
a wire in a thin tape form having a thickness of about 0.3 mm, as
shown in FIG. 1 to FIG. 3. This FFC is manufactured by feeding
straight a conductor group "2a" formed by a singular to several
tens of conductors "a" arranged parallel with each other, putting
this conductor group 2a between nonconductive plastic films "b"
with adhesives from upper and lower side thereof, and laminating
this with a pair of upper and lower hot rolls "c".
[0005] A nonconductive plastic tape "e" is passed through an
adhesive tank "d", so that the plastic film "b" of the upper side
is obtained in accordance with the coating of adhesive at least on
an inner surface of the plastic tape "e".
[0006] Such a FFC in a tape form has normally excellent
flexibility. Hence, this is necessary and indispensable,
particularly as a wiring material for cable reel type rotating
connectors of automobile airbags, other than wiring materials for
movable parts in circuits of electric and electronic
equipments.
[0007] This is used by storing the FFC in a curled or U-shaped form
in a steering case, wherein bending life of about 1.times.10.sup.6
to 5.times.10.sup.6 is required in the bending radius R of from 5
to 15 mm in the temperature range of about -40 to 85.degree. C.
(the U-shaped sliding and bending test: in accordance with
JIS-C5016).
[0008] Recently, automobile airbags having high functions such as
finely controlling the way of swelling of the airbag depending on
the energy at the time of collision or the weight of a driver have
been developed, which entail a so-called multi-conductor FFC, in
which the number of conductors is increased to higher than twice
the number in the related art. However, as shown in FIG. 4, if the
number of conductors is simply increased, the width of the cable
increases, and the steering case or the like for storing this
becomes also large. Therefore, it can be considered to thin the
conductor itself, without changing the width of the cable. However,
since heavy current of several amperes is normally applied to the
FFC for automobile airbags, generation of heat attributable to an
increase in the conductor resistance becomes large, with a decrease
of a sectional area of the conductor due to thinning.
[0009] Therefore, in order to achieve multi-conductor cables
without changing the cable width and the conductor resistance from
those of the related art, it is necessary to ensure the same
sectional area as that in the related art, by making the thickness
of the cable thick and making the conductor thick in the thickness
direction.
[0010] However, if the thickness of the cable and the conductor is
made thicker than that of the conventional FFC, there is caused a
problem in that the flexibility which is the largest feature of the
flat cable decreases considerably. For example, if the conductor
thickness of the FFC is made twice as thick as that of the
conventional FFC, the flexibility thereof generally decreases up to
one tenth or below, and hence the flexibility required for the FFC
for automobile airbags cannot be satisfied.
SUMMARY OF THE INVENTION
[0011] The present invention has been proposed in order to
effectively solve such problems, and it is an object of the present
invention to provide a new bending-resistant flexible flat cable
that can exhibit flexibility equal to or higher than that of the
conventional FFC, even if the number of conductors is increased,
and the production process thereof.
[0012] In order to solve the above problems, the present invention
is a bending-resistant flexible flat cable integrated by
sandwiching a single or a plurality of flat type conductors between
plastic films with adhesives, wherein the conductor is formed of
pure copper having a wiredrawing draught of at least 95% and
elongation of at least 5%, or a solution-type high-conductivity
copper alloy having a conductivity of at least 70%, the plastic
film with adhesives is formed of one having a modulus of
longitudinal elasticity of at least 280 kg/mm.sup.2 and an
elongation of at least 80%, and the 180.degree. peel strength
between the adhesives of the plastic films with adhesives and the
conductor is made to be at least 0.8 kg/cm.
[0013] As a result, even if the number of conductors is doubled,
while keeping the current value of the conductor resistance, the
bending-resistant characteristic equal to or higher than that of
the conventional FFC can be exhibited.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 4 is a conception diagram showing one example in which
the number of conductors of a conventional flexible flat cable is
simply doubled;
[0015] FIG. 5 is an enlarged sectional view showing one embodiment
of a bending-resistant flexible flat cable according to the present
invention;
[0016] FIG. 6 is a diagram showing a method of evaluating the
bending-resistant characteristic adopted in this example;
[0017] FIG. 1 is an enlarged sectional view showing one embodiment
of a conventional flexible flat cable;
[0018] FIG. 2 is a conception diagram showing a production process
of a conventional flexible flat cable; and
[0019] FIG. 3 is a conception diagram showing the production
process in FIG. 2, as seen from above.
EMBODIMENTS OF THE INVENTION
[0020] One preferable embodiment of the present invention will now
be described with reference to the accompanying drawings.
[0021] FIG. 1 is an enlarged sectional view showing one embodiment
of a bending-resistant FFC1 for automobile airbags according to the
present invention.
[0022] As shown in this figure, this FFC1 is formed by sandwiching
a plurality of flat type conductors 2,2 . . . arranged at the same
pitch between a pair of plastic films 3 with adhesives from upper
and lower sides thereof. The cable width thereof is substantially
the same as that of the conventional FFC for automobile airbags,
but the number and the thickness of the conductors 2 are nearly
doubled compared to those of the conventional FFC to thereby form a
narrow-pitch multi conductors.
[0023] This flat type conductor 2 is formed of pure copper such as
OFC (oxygen-free copper) or TPC (tough pitch copper), or a cheap
solution-type high-conductivity copper alloy having a conductivity
of at least 70%, similar to that of the related art. The
wiredrawing draught thereof has heretofore been 80 to 90%, but in
the present invention, a copper alloy annealed and refined so as to
have an elongation of 5% or more, after high processing of at least
95%, and preferably, at least 99%, is used. That is to say, the
reason why the elongation of this conductor 2 is defined as 5% or
more is that in the case of applying this conductor for automobile
airbags, in many cases, the vicinity of the end portion thereof is
bent for use, and hence, if the elongation of the conductor 2 is
less than 5%, the conductor 2 cannot endure the flexural strain at
the time of bending the end portion, and there is a possibility of
a rupture. Moreover, the reason why the conductivity of this
conductor 2 is defined as at least 70% is to solve problems caused
by an increase of the thickness of the conductor 2, with an
increase of conductivity, if it is assumed that the resistance is
constant, for example, (1) since the flexural rigidity of the
conductor 2 increases in proportion to the cube of the thickness
thereof, the flexibility as the FFC considerably decreases; (2)
since the FFC is used in many cases by bending the vicinity of the
end portion thereof, the bending resistance of the FFC considerably
decreases with an increase of the thickness of the conductor 2; and
(3) the weight of the FFC increases.
[0024] This flat type conductor 2 has preferably a width of from
0.3 to 1.0 mm and a thickness of from 50 to 100 .mu.m. As the
production process thereof, for example, after a round bus bar
having a diameter of about 8 mm is subjected to cylindrical dies
wire drawing to substantially the same area as that of the final
shape without annealing, the obtained intermediate material is
subjected to precise rectangular rolling, annealing and refining to
the final geometry, to thereby obtain this flat type conductor very
easily. This wiredrawing draught is defined by the following
expression:
Wiredrawing draught=(1-sectional area of flat type
conductor/sectional area of round bus bar).times.100(%).
[0025] As this solution-type high-conductivity copper alloy, there
is used a copper alloy in which at least one kind of Sn or In is
added in Cu in a small amount of from 0.05 to 0.5% in total.
[0026] On the other hand, the plastic films 3 with adhesives have
heretofore had a modulus of longitudinal elasticity of from about
200 to 230 kg/mm.sup.2, but in the present invention, a plastic
film having a modulus of longitudinal elasticity of at least 280
kg/mm.sup.2, and preferably at least 300 kg/mm.sup.2, and having an
elongation of at least 80%, and preferably at least 100% is used.
That is to say, if the modulus of longitudinal elasticity is less
than 280 kg/mm.sup.2, and the elongation is less than 80%, the
flexibility equal to that of the conventional FFC cannot be
obtained. Elongation ref erred to herein is an elongation value at
which a film is not peeled off from the adhesives, or a crack does
not occur in the adhesives, during a tensile test of the film with
adhesives. Moreover, in the FFC for automobile airbags, since there
may be a case where the temperature of use environment reaches
85.degree. C. at maximum, and may reach 100.degree. C. according to
circumstances. Therefore, it is desired to add, in the adhesives, a
thermoplastic and a flame retardant, and further a thermal
crosslinking agent (thermosetting agent) in view of heat
resistance. Specifically, there can be mentioned polyethylene
terephthalate (PET), polyethylene naphthalate (PEN), polyphenylene
sulfide (PPS) or polyetherimide (PEI), with flame retardant
polyester type adhesives. Among these, in view of the cost aspect,
it is desired to use PET, but if giving much weight to the flexuous
property, it is desired to use PEN or PPS having higher elasticity
than PET. Also, since PEI itself has excellent self extinguish, if
this PEI is used, it becomes possible to decrease the amount of use
of the flame retardant in the adhesives which decreases the
bending-resistant characteristic, thereby excellent
bending-resistant characteristic can be exhibited.
[0027] Moreover, the 180.degree. peel strength between the
conductor 2 and the adhesives is at least 0.8 kg/cm, and preferably
at least 1.0 kg/cm. It is because if it is less than 0.8 kg/cm,
problems such as peeling may occur with repeated bending. This
180.degree. peel strength is determined by the tensile test (at a
rate of 20 mm/min.) of the conductor in an exposed portion thereof
at the end of the FFC.
[0028] In the case of FFC1 of the present invention, as
demonstrated in the Examples described below, even if the
conductors 2 are arranged in a narrow pitch and the number thereof
is considerably increased compared to the conventional FFC,
accompanying the high-function airbags, excellent bending-resistant
characteristic equal to or higher than that of the conventional FFC
can be exhibited, without causing problems such as an increase of
electric resistance.
[0029] With such a production process of FFC, as in the related art
shown in FIG. 1 and FIG. 2, after thermocompression bonding of the
conductor 2 and the plastic films 3 with adhesives with hot rolls,
the adhesives are cured in a heating furnace such as oven for
several hours to tens of hours, thereby enabling easy production.
Also the FFC1 of the present invention is applicable as a harness
for automobile doors which requires bending resistance, and by
application of this FFC1, the harness can be formed in
multi-circuits and in light weight.
EXAMPLES
[0030] In order to verify the effects of the present invention,
several types of FFCs different in the processing conditions of
conductors and in the mechanical properties of the adhesives of the
plastic film were made for trial purposes, as shown in Table 1 and
Table 2 below, and the bending-resistant characteristics thereof
were evaluated.
[0031] As the plastic films with adhesives used herein, PET
(polyethylene terephthalate) with flame retardant polyester type
adhesives having different modulus of longitudinal elasticity and
elongation was used for each case, and the thickness of PET was
designated as 50 .mu.m and the thickness of the adhesives was
designated as 30 .mu.m (including the thickness of anchor
coat).
[0032] The evaluation method of this bending-resistant
characteristic is in accordance with JIS-C5016. As shown in FIG. 3,
the obtained FFC1 is bent in a U-shape, with one end being attached
to the tip of a driving plate 4, and the other end being fixed to
stationary plates 5, using fixation metal fittings 6, then the
driving plate 4 is repeatedly reciprocated in constant strokes in
the direction of arrows in the figure, and the fatigue life until
the conductors in the FFC1 have been cut is measured by a detection
apparatus (not shown). In the figure, reference numeral 7 denotes a
terminal for connecting the end of the FFC 1 with the disconnection
detection apparatus.
[0033] The specific conditions in this evaluation are as
follows:
[0034] Bending Life Measuring Conditions
[0035] Bending speed V: 1500 rpm
[0036] Stroke S: 25 mm
[0037] Distance H between parallel flat boards: 16 mm
(corresponding to bend radius R=8 mm)
[0038] Environmental temperature: 23.degree. C.
[0039] Detection of bending life: number of times until the
energizing current of the conductor for a monitor stops for more
than 10.sup.-6 seconds or the conductor resistance is increased by
10% from the initial state
[0040] Pass or fail condition of bending life: higher than the
conventional conditions
[0041] On the other hand, the mechanical properties of the plastic
film with adhesives, which vary largely depending on the measuring
conditions, were measured by a tensile tester under the conditions
of a gage length of 30 mm, a sample width of 10 mm, and an elastic
stress rate of 4 mm/min.
EXAMPLES
[0042] As shown in Table 1, twelve conductors having a wiredrawing
draught of at least 95% and an elongation of at least 5% were used,
which were sandwiched between plastic films with adhesives having a
modulus of longitudinal elasticity of at least 280 kg/mm.sup.2 and
an elongation of at least 80%, with the stroke width and the pitch
being 0.5 mm and 1.0 mm, respectively, and were subjected to thermo
compression bonding. Thereafter, the adhesives were cured in a
heating furnace such as oven for several hours to tens of hours, to
thereby prepare ten kinds of FFC samples for tests, and the
respective bending lives were evaluated on the basis of the bending
life of the FFC samples for tests according to the related art
described below.
[0043] (Related art)
[0044] As shown in the column (No. 11) of the related art in Table
2 described below, FFC samples for tests were prepared in the same
manner as that of the Examples, with the exception that six
conductors having a wiredrawing draught of 85% and an elongation of
26% were used, which were sandwiched between plastic films with
adhesives having a modulus of longitudinal elasticity of 218
kg/mm.sup.2 and an elongation of 132%, with the stroke width and
the pitch being 1.0 mm and 2.0 mm, respectively, and the respective
bending lives were evaluated.
Comparative Examples
[0045] As shown in the columns (No. 12 to No. 17) of Comparative
Examples in Table 2 described below, six kinds of FFC samples for
tests were prepared in the same manner as that of the Examples,
with the exception that conductors having a wiredrawing draught of
at least 85% and an elongation of at least 23% were used, which
were sandwiched between plastic films with adhesives having a
modulus of longitudinal elasticity of 218 to 320 kg/mm.sup.2 and an
elongation of 45 to 132%, and the respective bending lives were
evaluated.
1 TABLE 1 Examples (present invention) FFC characteristics No. 1
No. 2 No. 3 No. 4 No. 5 No. 6 No. 7 No. 8 No. 9 No. 10 Conductors
Material OFC Cu-0.15% Cu-0.2% OFC OFC OFC OFC OFC OFC OFC Sn
Sn-0.1% In Wiredrawing 95 95 95 99 99.9 95 95 95 95 95 draught (%)
Width (mm) 0.5 Thickness (.mu.m) 70 80 90 70 70 70 70 70 70 70
Tensile strength 23 28 32 22 24 35 28 23 23 23 (kg/mm.sup.2)
Elongation (%) 25 23 22 22 18 7 14 25 25 25 Films with Modulus of
285 285 285 285 285 285 285 337 320 318 adhesives longitudinal
elasticity (kg/mm.sup.2) Elongation (%) 120 120 120 120 120 120 120
82 94 103 FFC Number of cores, 12 samples for Lateral width, 0.5 mm
test Pitch 1.0 mm 180.degree. peel 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.1
0.9 0.8 strength (kg/cm) Bending life* .largecircle. .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle. *Bending
life was obtained by comparison with No. 11 (.largecircle.: equal
to or higher than that of No. 11, X: less than that of No. 11)
[0046]
2 TABLE 2 Related art Comparative Examples FFC characteristics No.
11 No. 12 No. 13 No. 14 No. 15 No. 16 No. 17 Conductors Material
OFC OFC OFC OFC OFC Cu.0.15% Cu.0.15% Sn Sn Wiredrawing draught (%)
85 85 95 95 95 85 95 Width (mm) 1.0 0.5 Thickness (.mu.m) 35 70 70
70 70 80 80 Tensile strength (kg/mm.sup.2) 24 24 23 23 23 29 28
Elongation (%) 26 26 25 25 25 26 23 Films with Modulus of
longitudinal 218 285 218 320 313 285 218 adhesives elasticity
(kg/mm.sup.2) Elongation (%) 132 120 132 45 96 120 132 FFC Number
of cores, 6 12 samples for Lateral width, Pitch 1.0 mm 0.5 mm test
2.0 mm 1.0 mm 180.degree. peel strength (kg/cm) 1.3 1.2 1.3 1.1 0.6
1.2 1.3 Bending life* -- X X X X X X *Bending life was obtained by
comparison with No. 11 (.largecircle.: equal to or higher than that
of No. 11, X: less than that of No. 11)
[0047] As a result, as shown in the bottom column of Table 1, in
the FFC sample for tests of each Example, the bending life thereof
exhibited properties equal to or higher than those of the
conventional FFC.
[0048] On the other hand, in No. 12 and No. 16 of Comparative
Examples where the wiredrawing draught of the conductor (85%) was
below the specified value of the present invention, in No. 13 and
No. 17 where the modulus of longitudinal elasticity of the plastic
film (218 kg/mm.sup.2) was below the specified value of the present
invention, in No. 14 where the elongation of the conductor (45%)
was below the specified value of the present invention, and in No.
15 where the 180.degree. peel strength (0.6 kg/cm) was below the
specified value of the present invention, the bending life thereof
was considerably inferior to that of the conventional FFC,
respectively.
[0049] As a result, it has been verified that by using conductors
consisting of pure copper having a wiredrawing draught of at least
95% and elongation of at least 5%, or a solution-type
high-conductivity copper alloy having a conductivity of at least
70%, using plastic films with adhesives having a modulus of
longitudinal elasticity of at least 280 kg/mm.sup.2 and an
elongation of at least 80%, and making the 180.degree. peel
strength between the adhesives of the plastic films with adhesives
and the conductor at least 0.8 kg/cm, the bending-resistant
characteristic becomes equal to or higher than that of the
conventional FFC, even if the number of conductors is doubled,
while keeping the current value of the conductor resistance.
[0050] Briefly speaking, according to the present invention, since,
even when the number of circuits is increased up to two times while
the current value of the conductor resistance is being maintained,
the bending-resistant characteristic with the conventional value or
more can be obtained, such an excellent effect can be achieved that
a large contribution to a development of an airbag for an
automobile having an excellent bending-resistant characteristic and
a high function required for narrow pitch and multi-line
orientation can be achieved and so on.
* * * * *