Wear-resistant insulating composition and wire

Abstract

To provide a composition having very high wear resistance sufficient to pass the scrape abrasion test in accordance with ISO6722.SOLUTION: A composition comprises a polytetrafluoroethylene micro powder having a particle size of 1 to 25 μm that is mixed with a base polymer comprising an ethylene-tetrafluoroethylene copolymer and a tetrafluoroethylene-propylene copolymer, wherein 0.8 pt.wt. or more and 5 pts.wt. or less of the polytetrafluoroethylene micro powder is mixed with 100 pts.wt. of the base polymer. A wire comprises a coating composed of the above composition formed on the outer periphery of a conductor wire. In the wire, the above coating may be crosslinked.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an abrasion-resistant insulating composition that is particularly suitable as an insulating material or sheath material, and an electric wire coated with the same. [Background technology]

[0002] Among fluoropolymers, ethylene-tetrafluoroethylene copolymers have extremely excellent mechanical strength, and it is known that crosslinking improves the heat resistance of the mechanical strength. It has also been disclosed that mixing ethylene-tetrafluoroethylene copolymers with polytetrafluoroethylene micropowder can provide a composition that combines excellent mechanical strength and heat resistance (see, for example, Patent Documents 1 and 2).

[0003] It is also known that when mixing the composition, tetrafluoroethylene micropowder is mixed with vinylidene fluoride-based fluororubber in advance, and then ethylene-tetrafluoroethylene is mixed with polytetrafluoroethylene micropowder and vinylidene fluoride-based fluororubber to facilitate the mixing process (see Patent Documents 2 and 3). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 10-67904: Kurabe [Patent Document 2] JP 11-105097: Kurabe [Patent Document 3] Patent No. 3897373: Kurabe Summary of the Invention [Problem to be solved by the invention]

[0005] The compositions described in Patent Documents 1 and 2 above have a problem of poor mixing and are difficult to produce. In addition, the compositions described in Patent Documents 2 and 3 are prone to unintended coloring during extrusion molding and crosslinking, making production difficult or imposing limitations on the choice of coloring.

[0006] In recent markets, there has been a demand for the ability to pass abrasion tests in order to prove the durability required for long-term use in environments such as engine rooms with a lot of vibration. The compositions described in Patent Documents 1 and 2 above have a problem of poor mixing, making them difficult to produce, and Patent Documents 2 and 3 above have unintended coloring, making them difficult to produce or limiting the color selection, making it difficult to meet customer demands. In addition, the compositions described in Patent Documents 1 to 3 above have not been used as thin-wall coatings for thin-walled electric wires, and sufficient consideration has not been given to the abrasion resistance of the compositions when used as thin-wall coatings for thin-walled electric wires.

[0007] The present invention has been made to solve such shortcomings of the prior art, and an object of the present invention is to provide a composition having such a high level of abrasion resistance that it passes the scrape abrasion test in accordance with ISO6722. [Means for solving the problem]

[0008] In order to achieve the above object, the composition according to the present invention is characterized in that a polytetrafluoroethylene micropowder having a particle size of 1 to 25 μm is mixed with a base polymer consisting of an ethylene-tetrafluoroethylene copolymer and a tetrafluoroethylene-propylene copolymer. It is also possible for the composition to be characterized in that polytetrafluoroethylene micropowder is mixed in the range of 0.8 parts by weight or more and 5 parts by weight or less with respect to 100 parts by weight of the base polymer. The electric wire according to the present invention may be characterized in that a coating made of the above-mentioned composition is formed around the outer periphery of a conductor wire. It is also contemplated that the coating may be crosslinked. Effect of the Invention

[0009] According to the present invention, it is possible to obtain a composition having a very high degree of abrasion resistance, such as passing the scrape abrasion test according to ISO6722. BEST MODE FOR CARRYING OUT THEINVENTION

[0010] When numerical values ​​are described in this specification, it means that the numerical value is rounded to the nearest digit. For example, the numerical value 6 includes a range of 5.5 to 6.4, the numerical value 0.8 includes a range of 0.76 to 0.84, and the numerical value 25 includes a range of 24.6 to 25.4.

[0011] As the ethylene-tetrafluoroethylene copolymer, binary copolymers having various polymerization ratios and multicomponent copolymers copolymerized with other fluorine-containing monomers are known, and any of them may be used.

[0012] The polytetrafluoroethylene micropowder is mainly used to improve the heat resistance and abrasion resistance of the resulting composition, and its particle size is preferably 1 to 25 μm. Since polytetrafluoroethylene micropowder is synthesized in water, if the particle size is small, it will not sink in water and cannot be separated from water. Therefore, it is difficult to stably produce a particle size smaller than 1 μm. In addition, polytetrafluoroethylene micropowder is generally granulated when it is distributed as a product. This is because if the polytetrafluoroethylene micropowder is in a fine powder state, it will aggregate over time and become secondary particles, which will deteriorate the appearance. There is a method called granulation break-down, in which the granulated polytetrafluoroethylene micropowder is broken down using a mixer or the like to produce fine powder of polytetrafluoroethylene micropowder. However, when polytetrafluoroethylene micropowder is processed using this method, the polytetrafluoroethylene micropowder is extremely shortened into short fibers. This shortened polytetrafluoroethylene micropowder is a particle that does not form fibers again during extrusion molding for coating electric wires, etc., and causes chipping of the coating during extrusion molding, resulting in poor appearance. Therefore, the particle size of the polytetrafluoroethylene micropowder is preferably 1 μm or more. Also, if the particle size is larger than 25 μm, the scrape abrasion resistance is reduced. This is because, when the polytetrafluoroethylene micropowder is mixed in a certain weight part with respect to the base polymer, the larger the particle size, the smaller the surface area ratio of the polytetrafluoroethylene micropowder in the composition. Therefore, the area ratio of the polytetrafluoroethylene micropowder on the friction surface also becomes smaller, and the abrasion resistance does not improve. For these reasons, the particle size of the polytetrafluoroethylene micropowder is preferably 1 to 25 μm.

[0013] There are various methods for measuring the particle size of polytetrafluoroethylene micropowder, such as the dry laser method, centrifugal sedimentation method, and sieving method. The particle size of the polytetrafluoroethylene micropowder according to the present invention is measured using the dry laser method and is defined as a particle size called the D50 median diameter. The D50 median diameter is the diameter at which the larger and smaller sides are equal in amount when the powder is divided into two parts at a certain particle size.

[0014] The tetrafluoroethylene-propylene copolymer acts to aid in the mixing of the ethylene-tetrafluoroethylene copolymer and the polytetrafluoroethylene micropowder. The mixing ratio of the ethylene-tetrafluoroethylene copolymer and the tetrafluoroethylene-propylene copolymer is preferably in the range of 96:4 to 98:2. If the mixing ratio of the ethylene-tetrafluoroethylene copolymer and the tetrafluoroethylene-propylene copolymer is within the above range, there is no problem of poor mixing, and the wear resistance is not reduced. The amount of polytetrafluoroethylene micropowder mixed is preferably 0.8 parts by weight or more and 5 parts by weight or less for 100 parts by weight of the base polymer consisting of an ethylene-tetrafluoroethylene copolymer and a tetrafluoroethylene-propylene copolymer. If the amount of polytetrafluoroethylene micropowder mixed is less than 0.8 parts by weight, the abrasion resistance decreases, and if it exceeds 5 parts by weight, the base polymer and the polytetrafluoroethylene micropowder will not mix properly. Therefore, it is particularly preferable to mix polytetrafluoroethylene micropowder in an amount ranging from 0.8 parts by weight to 5 parts by weight per 100 parts by weight of base polymer, since this makes it possible to obtain a composition which solves the problem of poor mixing.

[0015] It is particularly preferable that the particle size of the polytetrafluoroethylene micropowder is 6 μm. When the base polymers, ethylene-tetrafluoroethylene copolymer and tetrafluoroethylene-propylene copolymer, are mixed at the same ratio, the scrape abrasion resistance is most improved when the particle size of the polytetrafluoroethylene micropowder is 6 μm. Incidentally, this 6 μm is a particle size called the D50 median diameter. Also, the number 6 includes the range of 5.5 to 6.4.

[0016] To the composition of the present invention, various additives that are generally used, such as crosslinking assistants, lubricants, acid acceptors, silica powder, etc., can be appropriately added within the range that does not impair the properties such as flame retardancy and abrasion resistance. These various additives may be used alone or in combination.

[0017] As the crosslinking aid, ethylene glycol dimethacrylate, 1,3-butylene dimethacrylate, zinc methacrylate, trimethylolpropane trimethacrylate, triallyl cyanurate, triallyl isocyanurate, etc. may be added. In particular, triallyl isocyanurate is preferable from the viewpoint of improving crosslinking efficiency and heat resistance. By mixing 0.1 parts by weight or more and 4 parts by weight or less of the crosslinking aid with 100 parts by weight of the base polymer consisting of an ethylene-tetrafluoroethylene copolymer and a tetrafluoroethylene-propylene copolymer, it becomes possible to increase the crosslinking efficiency. If the amount mixed is less than 0.1 parts by weight, the effect of the crosslinking aid is not expressed, and if it exceeds 4 parts by weight, foaming is likely to occur during processing.

[0018] Examples of the lubricant include paraffin, hydrocarbon resin, fatty acid, fatty acid metal salt (metal soap), fatty acid amide, fatty acid ester, higher alcohol, etc. In particular, sorbitan tristearate, which is a fatty acid ester, is preferred from the viewpoint of improving workability. By mixing 0.02 parts by weight or more and 0.04 parts by weight or less of the lubricant with 100 parts by weight of the base polymer consisting of an ethylene-tetrafluoroethylene copolymer and a tetrafluoroethylene-propylene copolymer, the effect of improving workability during extrusion molding is achieved.

[0019] The composition of the present invention can be obtained by thoroughly kneading a mixture of the above-mentioned constituent materials using a known kneading machine such as an internal mixer, a single-screw kneader, or a twin-screw kneader.

[0020] The oil resistance of the composition of the present invention can be improved by crosslinking. The crosslinking method is not particularly specified, but a chemical crosslinking method using an organic peroxide or an electron beam crosslinking method using radiation energy can be used. Electron beam crosslinking is preferred as the crosslinking method. When electron beam crosslinking is used, the dose of electron beam is preferably 4 to 20 Mrad. A dose of less than 4 Mrad does not provide a sufficient degree of crosslinking, and a dose of 20 Mrad or more tends to reduce the elongation at break and the mechanical strength.

[0021] The composition of the present invention thus obtained can be extruded by a known method onto the outer periphery of a conductor wire to form a covering, thereby obtaining an electric wire according to another embodiment of the present invention. After the composition is extruded by a known method onto the outer periphery of a conductor wire to form a covering, the composition may be crosslinked as appropriate to improve the oil resistance of the composition. The covering may be a single layer or multiple layers. EXAMPLES

[0022] Examples of the present invention will be described below together with comparative examples. The components were mixed in the ratios shown in Table 1, and the resulting composition was used to cover a nickel-plated soft copper stranded wire with a conductor diameter of 0.35 sq to a thickness of 0.2 mm using a general-purpose wire extruder. The cover was then irradiated with an electron beam at an exposure dose of 4 Mrad to effect crosslinking.

[0023] The electric wire thus obtained was used as a sample and evaluated by the following evaluation methods. The results are shown in Table 1. The amount of each component in Table 1 is given in parts by weight.

[0024] The evaluation method is as follows. Abrasion resistance: A scrape abrasion test was conducted according to ISO 6722. The scrape abrasion test is evaluated using a device designed to rub a metal wire of 0.45 mm diameter in both directions along the longitudinal direction of the coating surface of the test sample, and a counter that records the number of cycles until the coating is broken. One cycle consists of one reciprocating motion, the length of the rub for one cycle is 15.5 mm, and 55 cycles are performed per minute. The pressure of the rub on the test sample is 7 N. The electric wires obtained in the examples were used as test samples and evaluated at a temperature of 23° C. Those for which the minimum number of cycles until the coating was broken was 150 or more were rated as ◯, and those for which the minimum number of cycles until the coating was broken was 149 or less were rated as ×.

[0025] [Table 1]

[0026] As shown in Table 1, the composition according to the present invention was confirmed to have a very high level of abrasion resistance. On the other hand, the comparative example in Table 1, in which the particle size of the polytetrafluoroethylene micropowder was larger than 25 μm, had a minimum scrape abrasion value of less than 150 times according to ISO 6722. [Industrial Applicability]

[0027] As described above, the composition according to the present invention not only solves the problem of poor mixing, but also has such a high level of abrasion resistance that it passes the abrasion resistance test according to ISO 6722. Therefore, it can be suitably used as various insulators, including insulating materials and sheath materials for electric wires and cables.

Claims

1. A composition comprising a base polymer consisting of an ethylene-tetrafluoroethylene copolymer and a tetrafluoroethylene-propylene copolymer, and a polytetrafluoroethylene micropowder having a particle size of 1 to 25 μm mixed therewith.

2. 2. The composition according to claim 1, wherein polytetrafluoroethylene micropowder is mixed in an amount of 0.8 parts by weight or more and 5 parts by weight or less per 100 parts by weight of said base polymer.

3. 3. An electric wire comprising a conductor wire and a coating made of the composition according to claim 1 or 2 formed around the periphery of the conductor wire.

4. 3. An electric wire comprising a conductor wire and a coating made of the composition according to claim 1 or 2 formed around the periphery of the conductor wire, the composition being crosslinked.

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