JP2022158408A - cable - Google Patents

Abstract

To extend the bending durability of a cable while using, as covering materials, insulating materials that are more inexpensive than fluorocarbon polymers.SOLUTION: A cable comprises a conductor covered with a resin composition, where the resin composition has a tensile stress of 25 MPa or more at an elongation of 40%-100%.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to a cable, and for example, to a cable with excellent bending resistance.

Japanese Patent Application Laid-Open No. 2008-218061 (Patent Document 1) describes a cable including a core wire in which the outer periphery of a conductor is coated with a thermoplastic resin as an insulator, in which the thermoplastic resin is composed of a polyester elastomer and an organic Techniques have been described for cables containing 0.5 to 3.0% by weight of high molecular weight silicone polymers.

Japanese Patent Application Laid-Open No. 2008-218061

For example, fluororesins, typified by ethylene-tetrafluoroethylene copolymer (ETFE), are widely used as insulators, which are coating materials for cables used in moving parts of industrial robots and the like. These fluororesins have the property of having a small coefficient of friction. Therefore, if a fluororesin is used as a covering material for a cable, the strain generated in the conductor covered with the insulator can be reduced due to slipping between the insulators when the cable is bent. As a result, it is thought that the bending life of the cable can be lengthened. However, it is desired to further lengthen the bending life of the cable.

Here, the flexing life of a cable is defined as the number of times of flexing required for the conductor wire to break in the flexing test and the resistance of the conductor wire to rise to a certain value.

Furthermore, since the fluororesin is more expensive than other insulating materials, there is a problem that the manufacturing cost of the cable increases. For this reason, it is desired to extend the flexing life of the cable while using an insulating material that is less expensive than the fluororesin as the covering material of the cable.

SUMMARY OF THE INVENTION An object of the present invention is to extend the bending life of a cable while using an insulating material that is cheaper than a fluororesin as a covering material.

A cable in one embodiment includes conductors coated with a resin composition. Here, the tensile stress at elongation of 40% to 100% of the resin composition is 25 MPa or more.

According to one embodiment, it is possible to lengthen the flexing life of the cable while using an insulating material that is cheaper than fluororesin as the coating material.

It is a schematic diagram which shows the structure which twisted six insulated wires. FIG. 3 is a cross-sectional view showing the structure of a cable; FIG. 4 is a cross-sectional view showing another configuration of the cable; It is a figure which shows the structure of a bending test typically.

In principle, the same members are denoted by the same reference numerals throughout the drawings for describing the embodiments, and repeated description thereof will be omitted. In order to make the drawing easier to understand, even a plan view may be hatched.

<Cable configuration>
FIG. 1 is a schematic diagram showing a structure in which six insulated wires are twisted together.

In FIG. 1, six insulated wires 10 are twisted together, and FIG. 2 shows a cable containing these six twisted insulated wires.

FIG. 2 is a cross-sectional view showing the structure of the cable.

As shown in FIG. 2, cable 100 is a multicore cable including six twisted insulated wires 10 . Each of the six insulated wires 10 has a conductor group 10a in which a plurality of conductors are twisted together, and an insulating layer 10b that is an insulator covering the conductor group 10a. The six insulated wires 10 are wound with a pressing tape 20, and a sheath 30, which is a protective layer, is formed so as to cover the outer circumference of the pressing tape 20. As shown in FIG. Although the cable 100 is configured in this manner, the configuration of the cable 100 is not limited to the configuration shown in FIG. 2, for example. As shown in FIG. may be provided. By providing the shield 40 , electromagnetic noise from outside the cable 100 can be suppressed from being superimposed on signals propagating through the conductor group 10 a inside the cable 100 .

<New knowledge discovered by the inventor>
For example, cables used in movable parts such as industrial robots are required to have a long bending life. For this reason, bend-resistant cables with a long bending life are used for cables used in movable parts such as industrial robots. A fluororesin is often used as the resin composition for covering the conductor wire in this bend-resistant cable. Because fluororesin has a small coefficient of friction, it can reduce the strain that occurs in the coated conductor when it is bent, and has a sufficiently high elastic modulus, so there is no concern about buckling. It is from.

Therefore, it is useful to use a fluororesin as a resin composition from the viewpoint of lengthening the bending life of a bend-resistant cable. However, since fluororesins are more expensive than other resin compositions, the use of low-priced resin compositions to replace fluororesins has been investigated. In this regard, techniques for lowering the friction coefficient by adding silicone to materials such as polyethylene, polypropylene, polybutylene elastomer, etc., which have a sufficiently high elastic modulus and are not susceptible to buckling, have been investigated. .

However, when a bending test was conducted on a bend-resistant cable using a resin composition in which the coefficient of static friction was lower than that of fluororesin by adding silicone to a polymer having crystals such as polyethylene and polypropylene, the result was as follows. Sufficient bending life could not be obtained. In other words, it has been considered effective to reduce the static friction coefficient of the resin composition in order to lengthen the bending life of a flexible cable. Conversely, this suggests that physical properties other than the coefficient of static friction of the resin composition most likely affect the flex life.

Therefore, the present inventors investigated the relationship between the various physical properties of the resin composition and the bending life, and found that the stress during necking (tensile stress at an elongation of 40% to 100%), which is a tensile characteristic of the resin composition, is the bending life. As a new finding, it has a strong impact on

For example, in the stress-strain curve of a crystalline resin composition, the region where the elongation is 40% to 100% is the region where the necking phenomenon occurs in many polymers having crystals. In this necking region, slip occurs between polymer molecular chains, and the present inventors speculate that the tensile stress during necking reflects the strength of intermolecular interaction. Also, the molecules in the amorphous portion have a higher tensile stress when they are partially in the glass state. If the intermolecular interaction is not sufficient, as a result of the relaxation of repeated bending stress and strain during the bending test, the stress received during bending concentrates at the relaxed location, damaging the conductor coated with the resin composition. It is considered that the flex life of the flex-resistant cable is shortened. In other words, if the intermolecular interactions are strong enough, the flex life of the flex resistant cable will be increased. From the above, the novel findings found by the present inventors are, qualitatively explained, a material having a high tensile stress at an elongation of 40% to 100%, which is the tensile property of the resin composition, that is, a resin composition. It is a finding that local stress concentration is avoided by using a material having a strong interaction between constituent molecules, and as a result, the flexing life of a flex-resistant cable is lengthened.

Therefore, the technical idea of the present embodiment, which has been conceived based on the above-described novel knowledge, will be described below.

<Features of the embodiment>
As described above, the new knowledge found by the present inventors is that if the tensile stress at the elongation of 40% to 100%, which is the tensile property of the resin composition, increases, the flex life of the flex-resistant cable will be extended. It is knowledge that it is possible to With regard to this point, the present inventor further conducted extensive studies based on this finding, and as a result, found the following quantitative findings.

That is, the characteristic point in the present embodiment is that, for example, in a stress-strain curve obtained by a tensile test, a cable using a resin composition having a tensile stress of 25 MPa or more at an elongation of 40% to 100% of the resin composition It consists of In this case, the bending life of the cable can be lengthened without using a fluororesin as the resin composition. That is, according to the characteristic point of the present embodiment, since expensive fluororesin is not used, it is possible to extend the bending life of the cable while reducing the manufacturing cost of the cable.

The tensile stress at an elongation of 40% to 100% is preferably 34 MPa or more. More preferably, it is 40 MPa or more.

However, if the tensile stress is too high, the elongation of the resin composition tends to decrease. It is desirable to be above.

Examples of resin compositions satisfying these conditions include PBT (polybutylene terephthalate) elastomers having a Shore D hardness of 70 or more, polyamide elastomers, polyamide 11, polyamide 12, and polyketones.

For example, PBT elastomers have significantly different mechanical properties depending on the ratio of hard and soft segments. Regarding this point, by adjusting the ratio of the hard segment and the soft segment to have a Shore D hardness of about 70, the PBT elastomer can have a tensile stress of 25 MPa or more at an elongation of 40% to 100%. , the elongation at break can be 200% or more.

Polyamide elastomers, like PBT elastomers, also have significantly different mechanical properties depending on the ratio of hard segments to soft segments. For example, by adjusting the ratio of the hard segment and the soft segment to have a Shore D hardness of about 70, even with a polyamide elastomer, the tensile stress at an elongation of 40% to 100% can be 25 MPa or more, and the fracture Elongation can also be 200% or more.

Polyamide 11 and polyamide 12 are resin compositions having strong intermolecular interactions due to amide groups and high strength. Therefore, polyamide 11 and polyamide 12 can have a tensile stress of 25 MPa or more at an elongation of 40% to 100% and an elongation at break of 200% or more.

Polyketone is a resin composition with strong intermolecular interaction due to ketone groups and high strength. Therefore, polyketone can have a tensile stress of 25 MPa or more at an elongation of 40% to 100% and an elongation at break of 200% or more.

Considering the materials described above, it is desirable that the upper limit of the tensile stress is 60 MPa, that is, the tensile stress is 60 MPa or less.

<Verification of effect>
Subsequently, according to the present embodiment, even without using a fluororesin as the resin composition, by using a resin composition having a tensile stress of 25 MPa or more at an elongation of 40% to 100% of the resin composition , verification results that prove that the bending life of a bend-resistant cable can be lengthened.

<<Bending test)>>
A bending test was performed on the cables 100 (Examples 1 to 6 and Comparative Examples 1 to 5) shown in FIG.

60 strands made of tin-plated annealed copper wire with an outer diameter of 80 μm are twisted together as a conductor, the insulators are those listed in Table 1 below, and the sheath is a resin composition made of soft PVC. board.

In the bending test, as shown in FIG. 4, the upper end of the cable 100 was fixed, a weight with a load W (7.5 N) was suspended from the lower end of the cable 100, and a bending jig was used to bend the cable 100 to the left and right. With the cable 200 attached, the cable 100 was bent so as to bend ±90° in the horizontal direction along the bending jig 200 . The bending radius R of bending was three times the outer diameter of the cable 100 . The bending speed was 60 times/minute, and the number of times of bending was counted as one reciprocation in the left-right direction. In addition, the cable was repeatedly bent, and the cable was checked for continuity at appropriate times. The flexing life was obtained as a relative value when the flexing life of Comparative Example 1 was set to 100.

<<Tensile stress and breaking elongation at elongation 40% to 100%>>
In accordance with JISK7161, an insulating dumbbell piece (sample) was prepared, and a tensile test was performed using a Tensilon universal testing machine under the conditions of a gauge line distance of 20 mm and a tensile speed of 200 mm / min. Tensile stresses at elongations of 40% to 100% for Comparative Examples 1 to 5 were obtained.

The n number of the sample was 3, and the average value was calculated to show the tensile stress at an elongation of 40% and the tensile stress at an elongation of 100% in Table 1. The tensile stress at an elongation of 40% to 100% was obtained by calculating the average value of the tensile stress at an elongation of 40% and the tensile stress at an elongation of 100%.

In addition, the elongation at breakage of the sample was obtained based on the following formula.

Breaking elongation (%) = 100 × (L - L0) / L0
L: Distance between gauge lines before test L0: Distance between gauge lines at break

<<Evaluation result>>
Table 1 is a table showing verification results.

<<<Comparative Example 1>>>
In Comparative Example 1, the flex life of a flex-resistant cable using a fluororesin ethylene-tetrafluoroethylene copolymer (ETFE) as a resin composition was evaluated. As a result of this evaluation, the tensile stress at an elongation of 40% to 100% was approximately 24 MPa. Then, the bending life result was set to 100.

<<<Comparative Example 2>>>
In Comparative Example 2, the flex life of a flex-resistant cable using high-density polyethylene as the resin composition was evaluated. As a result of this evaluation, the tensile stress at an elongation of 40% to 100% was approximately 15 MPa. The bending life in Comparative Example 2 was about 80 as compared with Comparative Example 1.

<<<Comparative Example 3>>>
In Comparative Example 3, the flex life of a flex-resistant cable using a resin composition in which the coefficient of static friction was lowered by adding silicone to high-density polyethylene was evaluated. As a result of this evaluation, the tensile stress at an elongation of 40% to 100% was approximately 15 MPa. The bending life in Comparative Example 3 was about 90 as compared with Comparative Example 1.

<<<Comparative Example 4>>>
In Comparative Example 4, the flex life of a flex-resistant cable using polypropylene as the resin composition was evaluated. As a result of this evaluation, the tensile stress at an elongation of 40% to 100% was approximately 17 MPa. The bending life in Comparative Example 4 was about 85 as compared with Comparative Example 1.

<<<Comparative Example 5>>>
In Comparative Example 5, the flex life of a flex-resistant cable using a PBT elastomer having a Shore D hardness of 55 as the resin composition was evaluated. As a result of this evaluation, the tensile stress at an elongation of 40% to 100% was approximately 15 MPa. The bending life in Comparative Example 5 was about 80 as compared with Comparative Example 1. From the above, it can be seen that in Comparative Examples 2 to 5, the flex life is shorter than in the case where the fluororesin is used in the resin composition.

<<<Example 1>>>
In Example 1, the flex life of a flex-resistant cable using a PBT elastomer having a Shore D hardness of 72 as the resin composition was evaluated. As a result of this evaluation, the tensile stress at an elongation of 40% to 100% was approximately 24 MPa. The flex life in Example 1 was about 110 as compared with Comparative Example 1.

<<<Example 2>>>
In Example 2, the flex life of a flex-resistant cable using a PBT elastomer with a Shore D hardness of 82 for the resin composition was evaluated. As a result of this evaluation, the tensile stress at an elongation of 40% to 100% was approximately 26 MPa. The flex life in Example 2 was about 115 when compared with Comparative Example 1.

<<<Example 3>>>
In Example 3, the flex life of a flex-resistant cable using a polyamide elastomer having a Shore D hardness of 80 as the resin composition was evaluated. As a result of this evaluation, the tensile stress at 40% elongation was about 35 MPa, the tensile stress at 100% elongation was about 34 MPa, and the tensile stress at 40% to 100% elongation was about 34.5 MPa. The flex life in Example 3 was about 120 as compared with Comparative Example 1.

<<<Example 4>>>
In Example 4, the flex life of a flex-resistant cable using polyamide 11 having a Shore D hardness of 71 as the resin composition was evaluated. As a result of this evaluation, the tensile stress at an elongation of 40% to 100% was approximately 40 MPa. The bending life in Example 4 was about 120 as compared with Comparative Example 1.

<<<Example 5>>>
In Example 5, the flex life of a flex-resistant cable using polyamide 12 having a Shore D hardness of 77 as the resin composition was evaluated. As a result of this evaluation, the tensile stress at an elongation of 40% to 100% was approximately 35 MPa. The flex life in Example 5 was about 115 when compared with Comparative Example 1.

<<<Example 6>>>
In Example 6, the flex life of a flex-resistant cable using a polyketone having a Shore D hardness of 71 as the resin composition was evaluated. As a result of this evaluation, the tensile stress at an elongation of 40% to 100% was approximately 45 MPa. The bending life in Example 6 was about 130 as compared with Comparative Example 1.

From the above, it can be seen that in Examples 1 to 6, the flex life is longer than in the case where the fluororesin is used in the resin composition. In other words, it is confirmed that the use of a resin composition having a tensile stress of 25 MPa or more at an elongation of 40% to 100% of the resin composition can lengthen the flex life of a flex-resistant cable.

As shown in Examples 1 to 3, when an elastomer is used for the resin composition, it is desirable that the Shore D hardness is 70 or more from the viewpoint of extending the bending life.

Although the invention made by the present inventor has been specifically described based on the embodiment, the invention is not limited to the above embodiment, and can be variously modified without departing from the gist of the invention. Needless to say.

REFERENCE SIGNS LIST 10 Insulated wire 10a Conductor group 10b Insulating layer 20 Holding tape 30 Sheath 40 Shield 100 Cable 200 Bending jig

Claims (5)

A cable comprising a conductor coated with a resin composition,
The cable, wherein the resin composition has a tensile stress of 25 MPa or more at an elongation of 40% to 100%. A cable according to claim 1, wherein
The cable, wherein the resin composition comprises any one of polybutylene terephthalate elastomer, polyamide elastomer, polyamide 11, polyamide 12, or polyketone. In the cable according to claim 1 or 2,
The cable, wherein the resin composition has a breaking elongation of 200% or more. In the cable according to any one of claims 1 to 3,
The cable is a multicore cable in which a plurality of insulated wires are twisted together,
Each of the plurality of insulated wires,
a conductor group obtained by twisting a plurality of the conductors;
the resin composition covering the conductor group;
a cable. In the cable according to any one of claims 1 to 4,
The cable, wherein the Shore D hardness of the resin composition is 70 or more.

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