JP2008066105A - Small-diameter electric wire cord - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a small-diameter electric wire cord which has superior bending resistance and in which electrical conduction is hardly cut off by an external force. <P>SOLUTION: In the electric wire cord in which a conductor is formed by making polybenzasol fiber a core part and winding a copper wire outside the core part, and in which the surrounding of the conductor is covered by a thermoplastic resin, the polybenzasol fiber has the following structure that as for the respective cross sections of the respective monofilament fibers in a polybenzasol multi filament, a convex ratio (%)=(number of a convex cross sectional fiber/constituting number of the multifilament)×100 is at least 75%. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an automobile, an electronic device, an audio device, a telephone cord, and an electronic computer represented by a super computer, a personal computer, a telephone exchange, a communication device, a mobile phone, a cardiac pacemaker, a camera, a hearing aid, a video camera, and a micromachine. The present invention relates to electric wire cords used for precision electronic equipment applications. More specifically, the present invention relates to a thin wire cord having a small diameter and high breaking strength.

  The structure of the electric wire cord is relatively simple, but it is used in a wide range of fields and used in various ways. In order to cope with this, materials for constituting the core have been studied conventionally. For example, Patent Document 1 uses a bending-resistant electric wire in which a metal stranded wire is horizontally wound on a fiber cord such as polyester or Kevlar (a product name made by DuPont), and Patent Document 2 uses an aramid fiber as a tension member. A thin wire is proposed in which a conductor is formed by concentrically twisting an annealed copper wire on the conductor, and the conductor is further covered with a synthetic resin insulator. Patent Document 3 and Patent Document 4 propose a small-diameter electric wire cord having improved soldering workability using a high-strength polyolefin fiber as a core.

Japanese Utility Model Publication No. 60-69420 Japanese Utility Model Publication No. 2-12113 JP-A-63-175303 JP-A-1-107415

In a thin wire using an aramid fiber for the core (tension member), a high-strength thin wire cord that could not be obtained by using a thin yarn with a high fineness since the fiber has high strength. can get. However, the aramid fibers are generally not melted by heating, and there is a drawback that when the wire cord is soldered to the terminal of the equipment, the end of the fiber becomes an obstacle and the soldering workability tends to be lowered. When heat-meltable polyester fiber is used for the core (tension member), the problem of poor solderability of the wire cord can be avoided, but it is inevitably used to satisfy the standard of tensile strength of the wire cord. It was necessary to increase the fineness of the fiber, and there was a limit to reducing the diameter of the wire cord.
When a high-strength polyolefin fiber is used for the core, the problems of soldering workability and diameter reduction of the wire cord can be solved because of the excellent heat melting property and high tensile strength of the fiber. However, since the coefficient of static friction resistance between the high-strength polyolefin fiber and the copper wire is low, the copper wire wound on the core made of the fiber is extremely slippery. Therefore, when the electric wire cord receives an extreme external force, the copper wire is broken before the core portion in the electric wire cord is broken, and the electrical conduction is interrupted. The problem is that the coefficient of static friction resistance between the fibers constituting the core part and the copper wire may be increased. As a specific means, the fiber constituting the core part and / or the copper wire may be coated with a resin having a high coefficient of static friction resistance. It can be solved to some extent. However, in order to perform resin coating treatment on the core or / and the copper wire, a dedicated coating facility is required, and the productivity of the electric wire cord is also reduced. Therefore, naturally, the manufacturing cost increases. Polyolefin fibers are difficult to adhere to resin, and when coating the core with resin, or when coating the resin as an insulator after winding the copper wire into a conductor, Delamination tends to be a problem.
Furthermore, along with recent downsizing and weight reduction of electronic devices, electronic circuits have become more complicated and smaller. For this reason, high flexibility has newly emerged as a required characteristic for a thin wire cord. Therefore, it has been expected to develop a fiber material that is less likely to be interrupted by an external force and can be reduced in diameter.
As described above, there are merits and demerits in using wholly aromatic polyamide fiber, polyester fiber and polyolefin fiber as the core part of the electric wire cord, and fibers that satisfy all the above requirements have not been industrially produced. .

  The present invention finds a suitable fiber material as a core (tension member) of a thinned wire cord, and provides a thin wire cord that has excellent bending resistance and is not easily interrupted by an external force.

The present invention employs the following configuration. That is,
1. A polybenzazole fiber is used as a core, and a conductor is formed by winding a copper wire on the outside of the core, and the conductor is coated with a thermoplastic resin, and the polybenzazole fiber is the following: A thin wire cord characterized by having a structure.
Polybenzazole fiber: Polybenzazole fiber: Polybenzazole The following convexity ratio (%) for each cross section of each monofilament fiber in the multifilament is at least 75%.
Convex ratio (%) = (number of convex cross-section fibers / number of multifilament components) × 100
2. When the cross section of the monofilament fiber is observed with an optical microscope, the sheath layer and the core layer can be distinguished from each other, and the ratio R (%) of the average diameter r ₂ of the core layer to the fiber cross sectional diameter r ₁ is 90. The thin wire cord according to claim 1, which is not more than%.

  According to the present invention, since the polybenzazole fiber with improved rigidity and improved bending durability is used for the core portion, a thin wire cord having a higher strength and flexibility (knot strength) is obtained. It is possible to provide a small-diameter electric wire cord that can meet demands such as high integration, complexity, and solderability.

Hereinafter, the present invention will be described in detail.
In the present invention, the polybenzazole fiber used for the core of the electric wire refers to a fiber made of a polybenzazole polymer, and the polybenzazole (hereinafter also referred to as PBZ) refers to polybenzoxazole (hereinafter also referred to as PBO), One or more polymers selected from polybenzothiazole (hereinafter also referred to as PBT) or polybenzimidazole (hereinafter also referred to as PBI). In the present invention, PBO refers to a polymer containing an oxazole ring bonded to an aromatic group, and the aromatic group is not necessarily a benzene ring, and may be a biphenylene group, a naphthylene group, or the like. PBO refers to a polymer containing an oxazole ring bonded to an aromatic group, but the aromatic group is not necessarily a benzene ring. Furthermore, PBO is not only a homopolymer of poly (p-phenylenebenzobisoxazole) but also a copolymer or aromatic in which a part of the phenylene group of poly (p-phenylenebenzobisoxazole) is substituted with a heterocyclic ring such as a pyridine ring. Polymers consisting of a plurality of oxazole ring units bonded to a group are widely included. The same applies to PBT and PBI. Also included are two or more mixtures of PBO, PBT and PBI, two or more block or random copolymers of PBO, PBT and PBI, and mixtures of these polybenzazole polymers, copolymers, block polymers, etc. .

  The structural unit contained in the PBZ polymer is preferably selected from lyotropic liquid crystal polymers that form liquid crystals at a specific concentration. The polymer consists of monomer units described in structural formulas (a) to (h), and preferably consists essentially of monomer units selected from structural formulas (a) to (d). In addition, these monomer units may partially include monomer units having a substituent such as an alkyl group or a halogen group.

  Suitable solvents for forming the polymer dope include cresol and non-oxidizing acids that can dissolve the polymer. Examples of suitable acid solvents include polyphosphoric acid, methanesulfonic acid and high concentrations of sulfuric acid or mixtures thereof. Further suitable solvents are polyphosphoric acid and methanesulfonic acid. The most suitable solvent is polyphosphoric acid.

  The polymer concentration in the dope is preferably at least about 7% by weight, more preferably at least 10% by weight, particularly preferably at least 14% by weight. The maximum concentration is limited by practical handling properties such as polymer solubility and dope viscosity. Due to their limiting factors, the polymer concentration usually does not exceed 20% by weight.

  In the present invention, suitable polymers or copolymers and dopes are synthesized by known methods. For example, Wolfe et al US Pat. No. 4,533,693 (1985.8.6), Sybert et al US Pat. No. 4,772,678 (1988.9.22), Harris US Pat. No. 4,847,350 (1989.7.11) or Gregory et al. U.S. Pat. No. 5,089,591 (1992.2.18). In summary, suitable monomers are heated in a non-oxidizing, dehydrating acid solution at a stepwise or constant rate of heating from about 60 ° C. to 230 ° C. under high-speed stirring and high shear conditions in a non-oxidizing atmosphere. It is made to react by raising.

  The dope polymerized in this way is supplied to the spinning section and discharged from the spinneret at a temperature of usually 100 ° C. or higher. A plurality of base pores are usually arranged in a circumferential shape or a lattice shape, but other arrangements may be used. The number of nozzle holes is not particularly limited, but it is important that the arrangement of the spinning holes on the spinneret surface has a hole density that does not cause fusion between the spun yarns (dope filaments).

  In order to obtain a sufficient draw ratio (SDR), the spun yarn needs a sufficiently long draw zone length as described in US Pat. No. 5,296,185, and has a relatively high temperature (above the solidification temperature of the dope). It is desirable that the air is uniformly cooled with a rectified cooling air having a temperature equal to or lower than the spinning temperature. The length (L) of the draw zone is required to be a length that completes solidification in a non-solidifying gas, and is roughly determined by the single-hole discharge amount (Q). In order to obtain good fiber properties, it is desirable that the draw zone take-out stress is 2.2 g / dtex or more in terms of polymer (assuming that only the polymer is stressed).

  It is important that the polybenzazole dope filament obtained above (stretched or unstretched) is contacted with a liquid vapor in which the polybenzazole is incompatible before being immersed in the coagulation bath. Thus, each cross section of each monofilament fiber constituting the polybenzazole multifilament can easily form a circular cross section, and the convexity ratio in the multifilament can be increased to 75% or more.

The convex ratio of the polybenzazole fiber used in the present invention is the ratio of the fiber of the convex cross section in the multifilament in each fiber cross section in the multifilament of the polybenzazole fiber. In addition, a convex cross section is a shape that can be touched only at one point no matter where the tangent line is drawn on the cross section of the cross section, and has no recess or dent in the main part of the contour line. It is a mold shape and is a cross section that can be considered to be almost circular. The cross section that does not correspond to the convex cross section is a cross section that has a concave portion or a dent in the main part of the outline of the cross section and that can draw a common tangent at two or more points (FIG. 1).
In the present invention, the fiber having a cross section that is almost circular to a perfect circle is 75% or more, so that the friction resistance between the fibers can be reduced. The convex ratio is preferably 80% or more, more preferably 85% or more, and further preferably 90% or more.

As a method for increasing the convexity ratio of the polybenzazole fiber used in the present invention, the polybenzazole fiber may be rapidly brought into contact with the coagulant before the deformation of the fiber cross section becomes large. Before dipping the dope filament (stretched or unstretched) in the coagulation bath, it is recommended to apply a steam treatment in which polybenzazole is actively contacted with a liquid incompatible with polybenzazole, that is, vapor of a coagulant. .
As a coagulant for polybenzazole, at least one of water, methanol, ethanol, acetone, and ethylene glycol is preferable, and water is more preferable in terms of simplicity.

  In the vapor treatment, the dope filament is positively brought into contact with the gas (air) containing the above-mentioned liquid vapor, so that the coagulant rapidly penetrates and diffuses throughout the fiber inside the dope filament, which is like a solidified nucleus. It is thought that is formed in the fiber center part direction. Surprisingly, when the fiber cross-section is observed after fiber formation, a boundary line that appears to be generated based on the difference in the timing of the start of structure formation is recognized, and so-called two-layer expression that can be expressed as a sheath core is recognized. It is done. The better the coagulant penetrates to the center, the smaller the core layer and eventually the borderline will not be recognized. It should be noted that a sheath / core structure is not recognized even in a conventional fiber not subjected to steam treatment.

The temperature of the steam treatment varies depending on the type of coagulant, but in the case of water, the temperature of the steam atmosphere or the temperature of the sprayed steam is preferably 50 to 200 ° C, more preferably 60 to 160 ° C. If it is less than 50 degreeC, the effect of reducing an intensity | strength will become small. On the other hand, when the temperature exceeds 200 ° C., yarn breakage frequently occurs and the productivity tends to be remarkably lowered. If the coagulant has a lower boiling point than water, the temperature may be lower, and if the coagulant has a higher boiling point than water, the temperature may be higher, and can be appropriately selected in consideration of the boiling point and the vapor pressure.
The content of the vapor component with respect to the total gas components in the vapor phase is preferably 50% by mass or more, more preferably 60% by mass or more, and further preferably 70% by mass or more for short-time treatment. .

If the vapor phase temperature is too low, the thickness of the sheath layer will not develop, and conversely if the temperature is too high, the sheath / core structure will appear, but the temperature of the passing filament will rise and the yarn will tend to break frequently. is there. If the vapor content is too low, the sheath / core structure is hardly developed.
The apparatus for performing the steam treatment is not particularly limited as long as the dope filament is in contact with the steam and can at least solidify the surface layer, and is not particularly limited to a continuous type, a non-continuous type, a sealed type, and a non-sealed type.

  The filament after passing through the vapor phase is then directed to a coagulation (extraction) bath for polybenzazole solvent extraction and complete coagulation of the filament. The coagulation bath is not particularly limited, and any type of coagulation bath may be used. For example, funnel type, water tank type, aspirator type or waterfall type can be used. Finally, extraction is performed so that the solvent remaining in the filament in the coagulation bath is 1% by mass or less, preferably 0.5% by mass or less. There is no particular limitation on the liquid used as the extraction medium in the present invention, but water, methanol, ethanol, acetone, ethylene glycol and the like that are substantially incompatible with polybenzazole are preferable. As the extract, an aqueous phosphoric acid solution or water is simple and desirable. Further, a method of separating the coagulation (extraction) bath in multiple stages, gradually decreasing the concentration of the phosphoric acid aqueous solution, and finally washing with water can be adopted. In the coagulation (extraction) step, it is a preferred method to neutralize the filament bundle with an aqueous sodium hydroxide solution and then wash with water. Thereafter, drying and heat treatment can be performed to obtain a fiber having a sheath / core structure.

  After that, the fiber is dried and further subjected to a heat treatment step as necessary. The drying temperature is not particularly limited as long as the coagulant or solvent of polybenzazole can easily fly, but specifically 150 to 400 ° C, preferably 200 to 300 ° C, more preferably 220 to 270 ° C. In order to improve the elastic modulus, heat treatment may be performed under tension as necessary. About heat processing temperature, it is 400-700 degreeC, Preferably it is 500-680 degreeC, More preferably, you may be 550-630 degreeC. The tension applied is 0.3 to 1.2 g / dtex, preferably 0.5 to 1.1 g / dtex, more preferably 0.6 to 1.0 g / dtex.

  Simple discrimination between the sheath layer and the core layer in the polybenzazole fiber used in the present invention is possible by observing the fiber cross section with an optical microscope. When the cross section of the fiber is magnified about 40 times with an optical microscope, the boundary between the sheath layer and the core layer is recognized as a circular line. The outer side of the circular line is a sheath layer, and the inner side is a core layer.

When the sheath layer is formed due to the penetration of the coagulant vapor, it is preferable that the thickness of the sheath layer is as large as possible and the diameter of the core layer is as small as possible. If steam treatment conditions are selected so that the steam penetrates and diffuses well, the ratio of the core layer can be lowered, and finally the ratio of the core layer can be reduced to 0%.
In the polybenzazole fiber used in the present invention, the ratio occupied by the core layer, that is, the ratio of the average diameter (r ₂ ) of the core layer in the fiber cross-sectional direction to the fiber cross-sectional diameter (r ₁ ) is R (%), It is preferably 90% or less, more preferably 80% or less, still more preferably 60% or less, and most preferably close to 0%. When R (%) exceeds 90%, fibrillation tends to occur and bending resistance tends to be insufficient.

  The reason why the polybenzazole fiber used in the present invention is difficult to fibrillate and the durability against bending is improved is not clear, but the orientation of the crystal of the sheath layer is appropriately disturbed by the action of steam and the direction of the fiber surface layer and the specific direction It can be inferred that the stress concentration on the surface is relaxed and fibrillation is suppressed.

Next, the thin wire cord using the polybenzazole fiber in the present invention will be described.
The reason why the electric wire cord is cut off from electrical continuity by an external force is that the copper wire is broken before the core portion in the cord is broken. According to Japanese Patent Laid-Open No. 1-107415, the breakage of the copper wire is If the static frictional resistance coefficient between the core forming the cord and the copper wire is at least 0.20 or more, this problem of interruption of electrical conduction can be avoided. Polybenzazole fiber is one of the fibers that meet this requirement. If this fiber is used, it is not necessary to coat the fiber or / and copper wire with a resin having a high coefficient of static friction resistance. As a result, it is advantageous in terms of product price. In addition, polybenzazole fiber has higher adhesion than high-strength polyolefin fiber, and the adhesiveness, that is, delamination in the wire cord coated with resin as an insulator is as high as when high-strength polyolefin fiber is used. Is not a problem.

  Next, the single yarn fineness, which is a requirement of the polybenzazole fiber used in the present invention, will be described. Conventionally, an electric wire cord formed by winding a copper wire on the core portion using a non-heat-meltable fiber as a core portion has difficulty in quick workability and soundness of the soldered portion when soldering to the equipment side terminal. It has been supposed to be. One means for solving this problem is the use of heat-meltable organic synthetic fibers. However, the present inventors can use a wire cord having a non-heat-meltable fiber as a core part by reducing the single yarn fineness of the fiber constituting the core part as much as possible and reducing the amount of fiber used. I found that no problem occurred. That is, one of the important constituent elements of the present invention is to arrange a polybenzazole fiber having a single yarn fineness of 1.1 dtex or less as a tension member in the core portion of the electric wire cord. When the single yarn fineness exceeds 1.1 dtex, the flexibility of the fiber bundle protruding from the center position of the cord is reduced when the cord is soldered to the terminal on the equipment side, so soldering workability and poor contact of the soldered portion Cannot be improved. There is no lower limit to the single yarn fineness of the fiber used for the core, and it is preferable that the fiber be as thin as possible. However, it may be set as appropriate in consideration of the difficulty of the spinning technique and the spinning production.

The electric wire cord has an outer diameter restriction and requires a certain level of breaking strength. For example, in an application field such as an earphone, when the wire cord diameter is 1 mm or less, a tensile strength of 3500 g or more is required, and assuming that the strength utilization factor of the core fiber in the cord is 0.87, the core portion is It is preferable that the relationship of the following formula 1 is established between the tensile strength (TS) of the constituting fibril and the total fineness (dtex) of the fiber.
TS x 1.1 dtex ≧ 4000 g (Formula 1)

  From this relational expression, the tensile strength and the total fineness of the fibers constituting the core may be set so that the tensile strength of the electric wire cord is 4000 g or more. This means that if the tensile strength of the fibers used as the tension member is high, the total This means that the fineness can be lowered, leading to a reduction in the diameter of the cord. From this point of view, the tensile strength of the fiber used as the tension member is one of the important requirements. In the present invention, it is preferable to use polybenzazole fiber having a tensile strength of at least 4.0 GPa from the viewpoint of reducing the diameter of the electric wire cord. As will be described later, when the tensile strength is less than 4.0 GPa, the fineness of the fiber is inevitably increased in order to obtain the strength required for the conductor (for example, the tensile strength of the earphone cord is 3500 g), and the wire cord diameter is reduced. If the polybenzazole fiber is suppressed in fibrillation and has improved flexibility and knot strength, the lower limit of the tensile strength is 3.2 GPa, preferably 3.5 GPa. It is possible to make an electric wire cord that meets demands such as increased complexity, complexity, and solderability.

  As described above, the outer diameter of the electric wire cord is restricted. For example, as a product standard such as an earphone, the cord diameter is required to be 1.0 mm or less. For example, when the standard thermoplastic resin coating layer thickness is 300 μm and the standard copper wire wound layer thickness is 60 μm when the wire cord diameter is 1.0 mm, the thickness (diameter) of the tension member fiber bundle is calculated. 280 μm. When this apparent fiber bundle diameter is converted into the fineness of the polybenzazole fiber, it corresponds to 935 dtex denier. If a polybenzazole fiber having a fineness less than or equal to a certain level and a tensile strength (for example, 4000 g or more) is used, it is possible to obtain a wire cord having a diameter of 1.0 mm or less.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these Examples.

<Intrinsic viscosity>
Using methanesulfonic acid as a solvent, the viscosity of the polymer solution prepared at a concentration of 0.5 g / l was measured in an oven at 25 ° C. using an Ostwald viscometer.
<Fiber fineness>
The single yarn fineness was measured at a sample length of 50 mm and a number of 20 using a Denicon (manufactured by Search Co., Ltd.) for a sample adjusted for 24 hours in an atmosphere of a temperature of 20 ° C. and a humidity of 65 RH%, and an arithmetic average value was obtained. . The total fineness was obtained by measuring the mass of the sample adjusted under the above conditions on a wrap reel by measuring 10 m and converting it to a mass of 9000 m.

<Method of fiber cross section observation>
A sample fiber embedded in an epoxy resin (G-2 manufactured by Gatan) was subjected to argon ion etching with a cross section polisher (SM-09010 manufactured by JEOL Ltd.) to obtain a fiber cross section for observation. . Next, the boundary line between the core layer and the sheath layer is observed with an optical microscope, the average diameter (r ₂ ) of the core layer and the fiber cross-sectional diameter (r ₁ ) are measured, and the average diameter (r ₂ ) of the core layer is measured. The ratio R (%) to the fiber cross-sectional diameter (r ₁ ) was determined.
R (%) = (r ₂ / r ₁ ) × 100

<Convex ratio>
The cross section of the fiber in the multifilament embedded in the epoxy resin prepared by the above method was observed with a scanning electron microscope. In addition, carbon vapor deposition was performed before observation, the Hitachi scanning electron microscope (model number S-4500) was used, the acceleration voltage was observed at 5-10 kV, and the magnification was 1000-3000 times.
When the tangent line is drawn at any point of the cross-section outline, it can be touched only at one point. The convex cross section is used. When the common tangent line can be drawn at two or more points of the outline, the cross section has a concave section. . The ratio of the fibers having a convex cross section in the multifilament was calculated.
Convex ratio (%) = (number of convex cross-section fibers / number of multifilament components) × 100

-Flexibility evaluation (measurement of relative nodule strength ratio):
After leaving in a test room in a standard condition (temperature: 20 ± 2 ° C, relative humidity (RH) 65 ± 2%) for 24 hours or more, the tensile strength, elastic modulus, and knot strength of the fiber are tested in accordance with JIS L 1015. Measured with a machine. The knot strength was measured by a tensile test in a state where one Z-twisted main knot was formed at the center of the holding interval of the sample. The relative nodule strength ratio was determined using the following formula.
Relative nodule strength ratio E (%) = (nodule strength / fiber strength) x 100

<Tensile properties of cord>
In accordance with JIS L 1013, using Tensilon manufactured by Orientec Co., Ltd., the grip distance was 20 cm, the tensile speed was 100% / min, and n = 10, and the tensile properties were obtained by personal computer processing.

<Measurement method of nodule strength>
In the state where one Z-strand main knot was formed at the center of the holding interval of the sample, the knot strength was evaluated by measurement according to the above-described tensile strength test method.

<Solderability evaluation method>
The quality of soldering was judged visually.

(Manufacture of fibers for comparative examples)
Using a spinning dope (PBO concentration of 14% by mass) in which poly (p-phenylenebenzobisoxazole) (hereinafter abbreviated as PBO) having an intrinsic viscosity [η] of 29 dl / g was dissolved in polyphosphoric acid, a single filament diameter Was spun under the conditions of 11.5 μm and 1.65 dtex.
That is, the spinning dope was spun from a nozzle with a spinning temperature of 175 ° C. and a pore diameter of 0.20 mm and a number of holes of 166, and the spun dope filament was cooled by passing through a quench chamber having a quench temperature of 60 ° C. and passed through the quench chamber. Then, it was immersed in the 1st coagulation | cleaning bath, making it converge on a multifilament, and the filament was coagulated. Thereafter, the filament was washed with water until the residual phosphorus concentration in the filament became 5000 ppm or less, neutralized with a 1% NaOH aqueous solution for 5 seconds, and further washed with water for 10 seconds. Then, it was dried until the moisture content became 2% and wound up to obtain a fiber for evaluation. As a result of measuring the cross section of the obtained comparative fiber, the R value was 100%, and the convex ratio was 72%.

(Manufacture of Example Fiber)
In the fiber manufacturing apparatus for the comparative example, a cylinder having an inner diameter of 5 mm and a length of 1 m is installed at the exit of the quench chamber, water vapor is introduced into the cylinder to fill the cylinder with a steam atmosphere, and the multifilament is allowed to pass through the cylinder. A fiber for evaluation was obtained in the same manner as in Comparative Example 1 except that the above was different.
The periphery of the cylinder was heated with a heater to control the water vapor temperature. The temperature of the filled water vapor was 75 ° C. saturated water vapor, and the time for the multifilament to pass through the water vapor atmosphere was 0.3 seconds.
The cross section of the obtained fiber for Example had an R value of 51% and a convex rate of 83%.

[Example 1 and Comparative Example 1]
Using each polybenzazole fiber manufactured for Examples and Comparative Examples as a core (tension member), 14 oxygen-free copper wire bundles coated with urethane on the core are wound to form a composite conductor. did. Next, the composite conducting wire was coated with polyvinyl chloride resin (PVC) to form an earphone cord. The obtained earphone cord was evaluated for solderability, cord diameter and the like. The evaluation results are shown in Table 1.

[Reference Example 1]
A thin wire cord was obtained in the same manner as in Example 1 except that a commercially available aramid fiber was used. The evaluation results are shown in Table 1.
[Example 2]
A fine wire cord was obtained by spraying urethane resin onto a core in which a monofilament was taken out from the yarn prepared in Example 1 and a monofilament was taken out and wound with a silver wire having a diameter of 5 μm. The evaluation results are shown in Table 1.

[Reference Example 2]
Instead of using polybenzazole fiber, a thin wire cord was obtained under the same conditions as in Example 1 except that a monofilament was taken out from the commercially available aramid fiber used in Reference Example 1. It was. The evaluation results are shown in Table 1.

  The thin wire cord obtained by the present invention is a thin wire cord with excellent strength and bending resistance (nodal strength), and can meet the demands for high integration, complexity, and solderability of circuits. Yes, it is useful as a code in the electric and electronic equipment fields.

It is explanatory drawing which shows the example of the convex cross section of the cross section of the polybenzazole fiber used by this invention, and the example of a cross section (cross section which is not a convex cross section) which has a recessed part which is not used by this invention. It is typical explanatory drawing which shows an example of the sheath core of the polybenzazole fiber cross section in this invention.

Explanation of symbols

r ₁ : Fiber cross-sectional diameter r ₂ : Diameter of the core layer

Claims (2)

A polybenzazole fiber is used as a core, and a conductor is formed by winding a copper wire on the outside of the core, and the conductor is coated with a thermoplastic resin, and the polybenzazole fiber is the following: A thin wire cord characterized by having a structure.
Polybenzazole fiber: The following convexity ratio (%) for each cross section of each monofilament fiber in the polybenzazole multifilament is at least 75%.
Convex ratio (%) = (number of convex cross-section fibers / number of multifilament components) × 100 When the cross section of the monofilament fiber is observed with an optical microscope, the sheath layer and the core layer can be distinguished from each other, and the ratio R (%) of the average diameter r ₂ of the core layer to the fiber cross sectional diameter r ₁ is 90. The thin wire cord according to claim 1, which is not more than%.

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