JP2024046946A - Cable for movable part and manufacturing method of cable for movable part - Google Patents

Abstract

To provide a cable for a movable part which has good bending line of the cable even while using an insulation material at lower cost than a fluororesin as a covering material.SOLUTION: A cable 100 for a movable part has a plurality of insulated wires 10 including conductor groups 10a covered with insulation layers 10b, wherein the insulation layer 10b is composed of a resin composition containing high density polyethylene as a base polymer, has a gel fraction of 30-60%, and a rating temperature of 105°C or higher.SELECTED DRAWING: Figure 2

Description

The present invention relates to a cable for a moving part and a method for manufacturing a cable for a moving part.

Generally, cables used in moving parts of industrial robots and the like are made up of multiple insulated wires, and fluororesins such as ethylene-tetrafluoroethylene copolymer (ETFE) are widely used as the insulator that covers these wires.

These fluororesins have the property of having a low coefficient of friction. For this reason, when fluororesins are used as the coating material for insulated electric wires, the insulators slide when the cable is bent, reducing the strain that occurs in the conductor coated with the insulator. In addition, because they have a sufficiently high elastic modulus, there is no risk of buckling, and as a result, it is believed that the flex life of the cable can be extended.

Here, the flex life of a cable is defined as the number of flexes required for the conductor to break and the conductor resistance to increase to a certain value during a flex test.

However, since fluororesin is more expensive than other insulating materials, cables that use fluororesin have the problem of high manufacturing costs. For this reason, there is a need to provide a cable that uses an insulating material that is less expensive than fluororesin as the coating material for the insulated electric wire, yet has a good flex life and is suitable for use in moving parts.

As an example of a cable that uses a material that is less expensive than fluororesin and has a good flex life, JP 2008-218061 A (Patent Document 1) describes technology related to a robot cable that includes a core wire whose outer circumference is covered with a thermoplastic resin as an insulator, where the thermoplastic resin is made of polyester elastomer and contains 0.5 to 3.0 mass % of an organic high molecular weight silicone polymer.

JP 2008-218061 A

The robot cable described in Patent Document 1 is said to improve the surface slipperiness between the insulated core wires and improve the bending and twisting life of the cable, but since it contains silicone polymer as an essential component, its applications may be limited. For example, in robots used in the manufacture of semiconductor devices, if silicone polymer is contained in the cable during the manufacture of the semiconductor devices, it may cause contamination, and the cable cannot be used for such applications.

The object of the present invention is to provide a cable for moving parts that uses an insulating material that is less expensive than fluororesin as a coating material, and yet has a good bending life, etc., for the cable that is applied to the moving parts as described above. In addition, it is preferable to provide a cable for moving parts that can also be used for manufacturing semiconductor devices.

In one embodiment, the cable for movable parts has multiple insulated wires including a conductor covered with an insulating layer, the insulating layer is made of a resin composition containing high-density polyethylene as a base polymer, the gel fraction of the insulating layer is 30 to 60, and the rated temperature is 105°C or higher.

In one embodiment, the method for manufacturing a cable for a movable part includes covering a conductor with a resin composition containing high-density polyethylene as a base polymer, forming an insulated electric wire having an insulating layer that is crosslinked by electron beam irradiation on the resin composition, and forming a protective layer by covering a plurality of the insulated electric wires with a sheath, and the irradiation intensity of the electron beam irradiation is 100 to 300 kGy.

According to one embodiment, in a cable applied to a moving part, it is possible to use an insulating material that is less expensive than fluororesin as the coating material, while still achieving good bending life characteristics for the cable.

FIG. 2 is a schematic diagram showing a structure in which six insulated wires are twisted together. FIG. 2 is a cross-sectional view showing the configuration of a cable. FIG. 11 is a cross-sectional view showing another configuration of the cable. FIG. 1 is a diagram showing a schematic configuration for a bending test.

In all drawings used to explain the embodiments, the same components are generally given the same reference numerals, and repeated explanations will be omitted. In addition, hatching may be used even in plan views to make the drawings easier to understand.

<Cable for moving parts>
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 for movable parts that includes these six twisted insulated wires. Fig. 2 is a cross-sectional view showing the configuration of the cable for movable parts.

As shown in FIG. 2, the cable 100 for movable parts is a multi-core cable including six twisted insulated wires 10. Each of the six insulated wires 10 has a conductor group 10a in which multiple conductors are twisted together, and an insulating layer 10b, which is an insulator that covers the conductor group 10a. The six insulated wires 10 are wrapped with a pressure tape 20, and a sheath 30, which is a protective layer, is formed to cover the outer periphery of the pressure tape 20.

The cable 100 is configured in this manner, but the configuration of the cable 100 is not limited to the configuration shown in FIG. 2, and can be applied to cases where the cable has two or more insulated wires 10 and the insulated wires 10 are in contact with each other. In a cable 100 configured in this manner, by using the insulated wire 10 in the movable portion as described in this embodiment, it is possible to ensure bending resistance and a good rated temperature, which is preferable.

Also, as shown in FIG. 3, a shield 40 may be provided between the pressure tape 20 and the sheath 30. By providing the shield 40, it is possible to prevent electromagnetic noise from outside the cable 100 from being superimposed on the signal propagating through the conductor group 10a inside the cable 100.

<New Findings Discovered by the Inventor>
In general, cables used in moving parts of industrial robots and the like are repeatedly bent in various directions due to the movement of the robots. Therefore, cables for moving parts are required to have a long flex life.

For this reason, cables made of resin with long bending life and resistance to bending are used for such movable parts, and as mentioned above, fluororesin is often used as the base polymer of the resin composition that forms the insulating layer that covers the conductor.

However, fluororesins are generally more expensive than other resin compositions, so there is a demand for low-cost alternatives to fluororesins that have good flex life.

In this regard, the present inventors have investigated alternative materials such as engineering plastics and have found that they can be used to improve the flex life. In particular, they have found that by increasing the degree of crosslinking in the engineering plastics, the stress during necking (tensile stress at an elongation of 40% to 100%), which is a tensile property of the resin composition, can be improved, and at the same time, the flex life can also be improved.

However, although engineering plastics are less expensive than fluororesins, they are still expensive materials and have not yet been sufficiently reduced in cost. Therefore, the inventors focused on high density polyethylene (HDPE) as a resin that is less expensive, is widely used, and has a sufficiently high elastic modulus, and investigated its use in cables for moving parts.

Specifically, we thought that by increasing the degree of crosslinking in high-density polyethylene, we could improve its flex life, just as we do in the above-mentioned engineering plastics. However, we discovered a new phenomenon in which increasing the degree of crosslinking in high-density polyethylene actually shortens its flex life.

On the other hand, high-density polyethylene is generally not used in a cross-linked manner as an insulating layer for insulated electric wires, and when not cross-linked, its rated temperature is as low as 80°C, making it unsuitable for use as a cable for moving parts used in a heated environment, such as in the manufacture of semiconductor devices.

The inventors have conducted extensive research and have discovered that by subjecting high-density polyethylene to a specific treatment, it is possible to provide a cable for movable parts that can be manufactured at low cost, has an improved rated temperature, can be used in the manufacture of semiconductor devices, and maintains good bending resistance.

The technical concept of this embodiment, which was conceived based on the novel findings described above, will now be described in detail.

<Features of the embodiment>
The movable cable of the present embodiment described above is characterized in that the insulating resin forming the insulating layer of the insulated wire therein has the following configuration.

[Insulating resin]
The insulating resin of this embodiment is made of a resin material (insulating material) obtained by subjecting a resin composition containing a polymer component with high density polyethylene (HDPE) as the base polymer to a predetermined crosslinking treatment. The resin composition used to form this insulating resin will be described in detail below.

(Resin composition)
(A) Polymer Component The polymer component used in the present embodiment contains high-density polyethylene as a base polymer, as described above. High-density polyethylene is a synthetic resin belonging to crystalline thermoplastic resins in which repeating units of ethylene are linearly bonded with almost no branching, and is polyethylene with a density of 0.942 or more. The melting point, density, and molecular weight of this high-density polyethylene are not particularly limited. High-density polyethylene is a component that has the effect of improving mechanical properties, and also has the effect of controlling the viscosity during extrusion molding.

"Containing high-density polyethylene as a base polymer" means that the content of high-density polyethylene is 50% by mass or more when the contained polymer component is 100% by mass. The content of high-density polyethylene is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 100% by mass.

The other polymers contained in the polymer component can be any polymer that does not inhibit the properties based on the high density polyethylene, and are not particularly limited. Examples of such polymers include low density polyethylene (LDPE), linear low density polyethylene (LLDPE), very low density polyethylene (VLDPE), ethylene-ethyl acrylate copolymer (EEA), ethylene-methyl acrylate copolymer (EMA), ethylene-vinyl acetate copolymer (EVA), ethylene-butene-1 copolymer, ethylene-octene copolymer, ethylene-propylene-diene terpolymer (EPDM), maleic acid modified polyolefin, and the like. These can be used alone or in combination of two or more.

(B) Crosslinking aid The resin composition used in the present embodiment is mainly composed of the above-mentioned polymer component, and may contain other components as desired. In the resin composition of the present embodiment, in order to form an insulating layer for an insulated wire, a conductor is coated with the resin composition, and then a crosslinking treatment is carried out. A crosslinking aid may be contained in order to efficiently proceed with the crosslinking treatment.

The cross-linking aid used here is a cross-linking aid for cross-linking treatment of high-density polyethylene, and known cross-linking aids such as trimethylolpropane acrylate (TMPT) and triallyl isocyanurate (TAIC (registered trademark)) can be used. Note that the cross-linking aid does not need to be contained in this resin composition and is an optional component.

(C) Other Components The resin composition used in the present embodiment may further contain other components as long as they do not impair the intended action. The other components are not particularly limited as long as they can be contained in this type of resin composition, such as antioxidants, flame retardants, lubricants, ultraviolet absorbers, light stabilizers, softeners, colorants, reinforcing agents, surfactants, inorganic fillers, plasticizers, metal chelating agents, foaming agents, compatibilizers, processing aids, and stabilizers.

(c1) Antioxidant The antioxidant can be used without any particular limitation as long as it is an antioxidant that is blended in this type of resin composition, and examples thereof include phenol-based antioxidants, phosphorus-based antioxidants, amine-based antioxidants, and sulfur-based antioxidants. Among these, phenol-based antioxidants and phosphorus-based antioxidants are preferred. The antioxidant used here may be used alone or in combination of two or more kinds.

Phenol-based antioxidants are not particularly limited, but examples include pentaerythrityl-tetrakis(3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene, etc.

Phosphorus-based antioxidants include, but are not limited to, tris(2,4-di-tert-butylphenyl)phosphite, bis(2,4-di-tert-butyl-6-methylphenyl)-ethyl-phosphite, etc.

Amine-based antioxidants include, but are not limited to, 4,4'-dioctyl diphenylamine, N,N'-diphenyl-p-phenylenediamine, and polymers of 2,2,4-trimethyl-1,2-dihydroquinoline.

Sulfur-based antioxidants include, but are not limited to, bis(2-methyl-4-(3-n-alkylthiopropionyloxy)-5-t-butylphenyl)sulfide, 2-mercaptobenzimidazole and its zinc salt, pentaerythritol-tetrakis(3-lauryl-thiopropionate), etc.

(c2) Flame retardant Examples of the flame retardant include metal hydroxides. The metal hydroxide is not particularly limited as long as it is a metal hydroxide known as a flame retardant, and examples thereof include magnesium hydroxide, aluminum hydroxide, calcium hydroxide, etc. Among them, magnesium hydroxide is preferable because the reaction temperature of the main dehydration reaction is as high as 350° C., and the flame retardancy of the insulating layer 10b is good.

The metal hydroxide is added in particulate form, and the particle size is preferably small. For example, it is preferable to use particles with an average particle size D50 in the range of 0.6 to 1.5 μm. In this specification, the average particle size refers to the particle size at 50% of the cumulative value in the particle size distribution determined by the laser diffraction/scattering method.

Taking into consideration dispersibility, the metal hydroxide can be surface-treated with a silane coupling agent, a titanate coupling agent, a fatty acid such as stearic acid, etc., and these can be used alone or in combination of two or more. To impart high heat resistance, it is preferable to perform surface treatment with a silane coupling agent.

(c3) Lubricant Examples of the lubricant include silicone additives. The lubricant is a component that reduces the static friction coefficient, smooths the sliding caused by contact between insulating layers, and also has the effect of improving the breaking elongation of the insulating layer. These components can be used alone or in combination of two or more.

The lubricant used here is not particularly limited and may be any known lubricant, for example, silicone additives such as organopolysiloxane. Examples of silicone additives include dimethylpolysiloxane, methylvinylpolysiloxane, methylphenylpolysiloxane, and modified polysiloxanes having functional groups such as vinyl groups at the terminals.

Note that silicone additives tend to reduce mechanical properties if added in excess, and because they are flammable, adding too much can reduce flame retardancy. Therefore, when silicone additives are added, the content is preferably 0.5 to 3.0 parts by mass per 100 parts by mass of the polymer component.

In the case of cables for moving parts used in the manufacture of semiconductor devices, silicone additives may cause contamination during the manufacture of the semiconductor device, so it is preferable that they are not substantially contained in such applications.

[Gel fraction]
As described above, in the present embodiment, the resin composition is cross-linked to form an insulating layer. At this time, the gel fraction of the insulating layer (the cross-linked resin constituting the insulating layer) is set to a range of 30 to 60%, preferably 35 to 50%.

The gel fraction represents the proportion of cross-linked polymer in the entire polymer. When a polymer is dissolved in a specific solvent, the portion that remains undissolved is considered to be gel (because the cross-linked portion remains as gel), and it is calculated as the ratio (percentage) of the mass of this gel portion to the mass of the polymer before it was dissolved in the solvent.

By setting the gel fraction at 30-60%, the resin constituting the insulating layer has a rated temperature of 105°C or higher and a flex life of 170,000 times or more, resulting in a resin material with excellent balance of properties. Such a resin material is suitable as a material constituting the insulating layer of insulated electric wires in cables for moving parts, particularly cables for moving parts of robots used in the manufacture of semiconductor devices.

The rated temperature is the maximum operating temperature at which the insulating resin maintains its functionality as a wire material for a specified period of time (without reaching the end of its life) when it is used continuously for a specified period of time (e.g., 3,000 hours or more) at a specified operating temperature.

The flex life was calculated as the number of flexes required to obtain a specified increase in resistance value in a specified flex test. The test conditions for this flex test are explained in the Examples section.

<Method of manufacturing a cable for a movable part>
The cable for movable parts of the present embodiment can be produced by a known method, except for obtaining an insulated wire having the insulating layer described above.

That is, first, a conductor, for example, a conductor formed by twisting wires together to form a conductor group 10a, is covered with a resin composition by a known method. The resin composition used here is the resin composition described above, which is used to form the insulating resin of this embodiment.

Next, a predetermined cross-linking process is performed on the resin composition that covers the conductor group 10a, thereby forming the insulating layer 10b as the outer layer of the insulated wire 10.

For the crosslinking treatment, for example, a crosslinking method using irradiation crosslinking in which an energy beam such as an electron beam or radiation is irradiated can be used. When performing irradiation crosslinking, a crosslinking assistant may be blended in advance into the resin composition, but in this embodiment, it is not necessary to blend a crosslinking assistant so as not to excessively increase the degree of crosslinking.

In addition, the irradiation intensity of the electron beam or radiation is preferably in the range of 100 to 300 kGy. By setting the irradiation intensity to 100 kGy or more, the rated temperature of the insulated wire can be increased to 105°C or higher. Furthermore, by setting the irradiation intensity to 300 kGy or less, excessive crosslinking can be suppressed, and in particular, the strength of the insulating resin used in the moving part can be ensured without excessively decreasing the bending resistance.

The resulting insulated electric wires 10 are twisted together, the outer circumference is wrapped with a pressure tape 20, and the outer circumference is further covered with a protective layer, a sheath 30, to produce a cable 100 for a movable part.

The cable obtained in this manner has a good flex life even though it does not use a fluororesin as the resin composition, and has an insulating layer that meets the rated temperature of 105°C or higher, making it suitable as a cable for moving parts. In other words, the cable for moving parts in this embodiment does not use expensive fluororesin, so the manufacturing cost of the cable can be significantly reduced, and a cable for moving parts with a long flex life can be provided.

Next, the movable part cable of this embodiment will be described in more detail with reference to examples and comparative examples.

(Examples 1-2, Reference Examples 1-2, Comparative Examples 1-6)
First, raw materials were prepared, and resin compositions were prepared according to the formulations shown in Tables 1 and 2. The raw materials used in the examples, reference examples, and comparative examples are as follows.

[material]
(A) Polymer (A1) High density polyethylene (HDPE): "Hi-Zex 5305E" (d: 0.951 g/cm ³ , MFR: 0.8), manufactured by Prime Polymer Co., Ltd.
(A2) Low-density polyethylene (LDPE): "UBE C450" manufactured by Ube Industries, Ltd.
(A3) Ethylene tetrafluoroethylene (ETFE)

(B) Crosslinking aid (B1) Trimethylolpropane triacrylate (TMPT)
(C) Antioxidant (C1) Antioxidant (AO): "AO-18" manufactured by Adeka Corporation

[Manufacturing of cables for movable parts]
The conductor was a strand of 60 tin-plated soft copper wires with an outer diameter of 80 μm, and the resin compositions forming the insulating layer shown in Tables 1 and 2 were used to cover the conductor by extrusion molding. The resin composition covering the conductor was then irradiated with 100 kGy or 300 kGy of electron beams to partially crosslink the resin composition to form an insulating layer, thereby obtaining an insulated wire.

The outer circumference of the obtained insulated electric wire was wrapped with a pressing tape, and the outer circumference was then covered with a sheath as a protective layer to produce a cable for movable parts. The sheath was formed using a resin composition made of soft PVC (soft polyvinyl chloride).

The following characteristic tests were carried out on the obtained movable cable, and the results are summarized in Tables 1 and 2.

<<Rated temperature>>
The rated temperature determined for each material in the UL standard was followed.

<<Bending test>>
Next, bending tests of the obtained cables 100 (Examples 1-2, Reference Examples 1-2, and Comparative Examples 1-6) were carried out under the following conditions.

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 hung from the lower end of the cable 100, and a bending jig 200 for bending the cable 100 left and right was attached. The cable 100 was then bent left and right along the bending jig 200 to bend it ±90°. The bending radius R was three times the outer diameter of the cable 100. The bending speed was 60 times/min, and the number of bendings was counted as one round trip in the left and right directions. The cable was repeatedly bent, and a continuity test was performed on the cable after each bending. The number of bendings at which the resistance value increased by 20% compared to the initial resistance value was determined as the bending life. The bending life was calculated as a relative value when the bending life of Comparative Example 1 was set to 100.

From the above results, it can be seen that in Examples 1 and 2, although the flex life is shorter than when fluororesin is used in the resin composition, a flex life of more than 170,000 times is ensured, and the flex life is sufficient for a cable for moving parts. In addition, it can be seen that the rated temperature of Examples 1 and 2 is 105°C, which is higher than that of Reference Example 1, which does not undergo crosslinking treatment.

The movable part cable of this embodiment therefore has a good flex life and an improved rated temperature, and has properties that allow it to be used as a movable part cable for robots used in the manufacture of semiconductor devices.

In addition, in Comparative Examples 1 to 6, the crosslinking process was further advanced compared to Examples 1 and 2, and the flex life was reduced, so it cannot be said that the cables are excellent for use in movable parts.

The invention made by the inventor has been specifically described above based on the embodiment thereof, but it goes without saying that the invention is not limited to the above embodiment and can be modified in various ways without departing from the gist of the invention.

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 (8)

A cable for a movable part having a plurality of insulated wires including a conductor covered with an insulating layer,
the insulating layer is made of a resin composition containing high-density polyethylene as a base polymer;
A cable for movable parts, wherein the insulating layer has a gel fraction of 30 to 60% and a rated temperature of 105° C. or higher. 2. The cable for movable parts according to claim 1,
The resin composition is a cable for a movable part, and contains, as a polymer component, at least one selected from low-density polyethylene, linear low-density polyethylene, very low-density polyethylene, ethylene-ethyl acrylate copolymer, ethylene-methyl acrylate copolymer, ethylene-vinyl acetate copolymer, ethylene-butene-1 copolymer, ethylene-octene copolymer, ethylene-propylene-diene terpolymer, and maleic acid-modified polyolefin. 2. The cable for movable parts according to claim 1,
The cable for movable parts contains the high-density polyethylene in an amount of 80 to 100% by mass when the polymer component contained in the resin composition is taken as 100% by mass. 2. The cable for movable parts according to claim 1,
the movable part cable is a multi-core cable in which the plurality of insulated electric wires are twisted together,
The cable for movable parts, wherein each of the plurality of insulated wires has a conductor group in which a plurality of the conductors are twisted together, and the insulating layer that covers the conductor group. A method for producing a cable for a movable part, comprising the steps of: covering a conductor with a resin composition containing high density polyethylene as a base polymer; forming an insulated electric wire having an insulating layer by crosslinking the resin composition by electron beam irradiation; and covering a plurality of the insulated electric wires with a sheath to form a protective layer,
The method for producing a cable for a movable part, wherein the electron beam irradiation has an irradiation intensity of 100 to 300 kGy. 6. The method for producing a cable for a movable portion according to claim 5,
A method for producing a cable for a movable part, wherein the insulating layer has a gel fraction of 30 to 60% and a rated temperature of 105° C. or higher. 6. The method for producing a cable for a movable portion according to claim 5,
The resin composition contains, as a polymer component, at least one selected from low-density polyethylene, linear low-density polyethylene, very low-density polyethylene, ethylene-ethyl acrylate copolymer, ethylene-methyl acrylate copolymer, ethylene-vinyl acetate copolymer, ethylene-butene-1 copolymer, ethylene-octene copolymer, ethylene-propylene-diene terpolymer, and maleic acid-modified polyolefin. 6. The method for producing a cable for a movable portion according to claim 5,
The method for producing a cable for a movable part includes the resin composition containing 80 to 100% by mass of the high-density polyethylene when the polymer component contained in the resin composition is taken as 100% by mass.

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