JPH0812767A - Heat-shrinkable electrical insulation tube - Google Patents

Abstract

PURPOSE:To obtain a heat-shrinkable electrical insulation tube excellent in elongation set, brittle fracture resistance, internal tack and hot-oil resistance by mixing a specified fluororesin with a thermoplastic fluoroelastomer and radiation-cross-linking the mixture. CONSTITUTION:This tube is made from a mixture prepared by mixing a composition containing a copolymer of tetrafluoroethylene with a 2-4C alpha-olefin (except ethylene) and a copolymer of tetrafluoroethylene with ethylene with a thermoplastic fluoroelastomer containing a fluoroelastomer in a weight ratio of 95:5 to 50:50 and cross-linked by irradiation with a radiation. It is desirable that the above mixture further contains 10-100 pts.wt. ethylene/chlorotrifluoroethylene copolymer and 20-50 pts.wt. inorganic filler per 100 pts.wt. above mixture. As the radiations used, electron beams, gamma-rays and beta-rays are desirable. The heighten the degree of cross-linking, it is possible to use a cross-linking aid.

Description

Detailed Description of the Invention

[0001]

[Industrial application] Fluorine-based elastomers have excellent heat resistance, oil resistance, and chemical resistance.
Widely used for packing, O-rings, hoses, etc. Due to such characteristics, there is also a high demand for use as an electrically insulating material such as a heat-shrinkable tube for terminal protection, and in recent years, as a fluoroelastomer exhibiting excellent characteristics in such an electric insulating field, tetrafluoroethylene-propylene copolymer Coalition was developed.

[0002]

However, when such a copolymer is used as an insulator in a heat shrinkable tube for electric wires, etc., the mechanical strength is low, it cannot be used as it is, and the crystal content in the copolymer is small. There was also a problem with the shape retention of the heat shrinkable tube.

Usually, in order to impart and improve the shape-retaining property (the tube is expanded and the shape is maintained as it is), addition of a crystalline polymer and co-crosslinking by electron beam irradiation are carried out. , Excellent in heat resistance, etc., the degree of decrease in the molecular weight of the polymer due to electron beam irradiation is small,
Ethylene-tetrafluoroethylene copolymer, polyvinylidene fluoride, vinylidene fluoride-fluoroolefin copolymer, ethylene-chlorotrifluoroethylene copolymer and the like are used (Japanese Patent Laid-Open No. 63-313411, Japanese Patent Laid-Open No. 63-13411). Sho 63-284713, Japanese Patent Publication No. 2-1
7341).

However, tetrafluoroethylene-
Fluorine-based elastomers such as propylene-based copolymers have a large permanent elongation, which is an indicator of the quality of rubber elasticity, and by blending with these polymers a resin material with a larger permanent elongation, the permanent elongation is further reduced. . Further, if a reinforcing agent is added to improve the permanent elongation, the elongation rate (rubber elasticity) is significantly reduced.

On the other hand, a fluorine-based thermoplastic elastomer has been developed as a fluorine-based material having elastomeric properties (Japanese Patent Laid-Open Nos. 61-20724 and 61-21114).

This elastomer is a polymer obtained by treating a hard segment made of a fluorine-based resin and a soft segment made of a fluorine-based rubber by dynamic cross-linking, and its mechanical properties are close to those of a conventional fluorine-based elastomer, and The tubes and the like formed from them have a drawback that brittle fracture is likely to occur under the condition where heat is applied simultaneously with stretching and compression, such as heat applied by winding.

Crosslinking by electron beam irradiation is considered as a means for suppressing this brittle fracture, but these fluorine-based thermoplastic elastomers tend to cause softening and deterioration of the tube surface due to electron beam irradiation, increasing the inner surface tackiness of the tube. In addition, heat resistance and oil resistance decrease due to deterioration of the tube surface.

This can be prevented to some extent by replacing the gas atmosphere around the tube with an inert gas such as N ₂ gas during electron beam irradiation (Japanese Patent Laid-Open No. 62-62).
146931, JP-A-62-146932, JP-B-5-18329). However, performing gas replacement to such an extent that the effect of oxygen dissolved in the tube can be ignored, or to the extent that internal tack does not occur, is actually a very complicated work and takes time.

This also applies to the case where the above crystalline polymer (fluorine resin) is blended. Since these fluorine resins and fluorine-based thermoplastic elastomers are inferior in cross-linking property to fluorine-based elastomers, the fluorine resin and the fluorine resin alone and the fluorine-containing resin are not used. Even in a blended system of a thermoplastic elastomer and a fluorine-based thermoplastic elastomer, the balance between cross-linking and molecular disintegration is easily lost, and improvement in internal tackiness and permanent elongation cannot be achieved.

[0010]

As described above, it is possible to improve the mechanical properties by blending a fluorine-based elastomer or a fluorine-based thermoplastic elastomer with a fluorine resin, but it is possible to improve the permanent elongation and brittle resistance. Destructiveness,
It was not possible to obtain a product having excellent internal tackiness, heat resistance and oil resistance.

It is an object of the present invention to provide a heat-shrinkable electrically insulating tube which is excellent in permanent elongation, brittle fracture resistance, inner surface tackiness and heat and oil resistance.

[0012]

Means for Solving the Problems As a result of repeated studies to solve the above problems, the present inventor has found that (A) tetrafluoroethylene and an α-olefin having 2 to 4 carbon atoms (excluding ethylene) It is conceived that a composition containing a copolymer and a copolymer of tetrafluoroethylene and ethylene and (B) a fluorine-containing thermoplastic elastomer containing a fluorine-containing elastomer component are blended and crosslinked by irradiation with radiation. The present invention has been completed.

That is, the present invention contains (A) a copolymer of tetrafluoroethylene and an α-olefin having 2 to 4 carbon atoms (excluding ethylene) and a copolymer of tetrafluoroethylene and ethylene. A composition comprising the composition and (B) a fluorine-based thermoplastic elastomer containing a fluorine elastomer component in a weight ratio of 95: 5 to 50:50, and being crosslinked by irradiation. A heat-shrinkable electrically insulating tube characterized by further comprising 10-100 parts by weight of ethylene-chlorotrifluoroethylene copolymer and 20 parts by weight per 100 parts by weight of the composition.
It is a heat-shrinkable electrically insulating tube containing ˜50 parts by weight of an inorganic filler.

In the present invention, as the α-olefin having 2 to 4 carbon atoms (excluding ethylene) to be copolymerized with tetrafluoroethylene, propylene, butene-1, isobutene, methacrylic acid and its alkyl ester, vinyl fluoride, Fluorovinylidene, hexafluoropropylene, chloroethyl vinyl ether, glycidyl vinyl ether, chlorotrifluoroethylene, perfluoroalkyl vinyl ether and the like can be mentioned, and these can be used alone or in combination of two or more kinds.

The hard segment of the fluorine-based thermoplastic elastomer containing the fluorine-based elastomer component is ethylene-tetrafluoroethylene copolymer,
Examples thereof include vinylidene fluoride and ethylene-chlorotrifluoroethylene copolymer, and as the fluoroelastomer component that becomes the soft segment, tetrafluoroethylene-α-olefin copolymer and vinylidene fluoride-propylene hexafluoride copolymer are used. Examples thereof include a combination, a vinylidene fluoride-tetrafluoroethylene copolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer and the like.

Here, (A) a composition containing a copolymer of tetrafluoroethylene and an α-olefin (excluding ethylene) having 2 to 4 carbon atoms and a copolymer of tetrafluoroethylene and ethylene. (B) The weight ratio with the fluorine-based thermoplastic elastomer containing the fluorine-based elastomer component needs to be 95: 5 to 50:50,
If the weight ratio of the thermoplastic elastomer is less than 95: 5, the value of permanent elongation cannot be improved, and if it exceeds 50:50,
The thermoplastic elastomer is likely to collapse upon irradiation with radiation, and the inner surface tackiness is deteriorated.

Further, in order to improve the low temperature embrittlement property, an ethylene-trichlorofluoroethylene copolymer may be added thereto in an amount of 10 to 10.
It is preferable to add 100 parts by weight (preferably 30 to 60 parts by weight) (Japanese Patent Publication No. 2-17341). If it is less than 10 parts by weight, the heat-setting property is deteriorated, and if it exceeds 100 parts by weight, the low temperature property is not improved.

The blending ratio of the copolymer of tetrafluoroethylene and the α-olefin (excluding ethylene) having 2 to 4 carbon atoms and the ethylene-fluoroolefin copolymer in the composition (A) is a weight ratio. 80: 20-50: 50
It is preferred that

The term "radiation" as used herein refers to X-rays, γ-rays, electron rays, proton rays, deuteron rays, α-rays, β-rays, etc., but electron rays, γ-rays or β-rays are preferably used.

Further, a cross-linking aid is used in order to achieve improvement in the degree of cross-linking. Examples of the cross-linking aid include allyl-type compounds, sulfur, organic amines, maleimides, methacrylates, divinyl compounds, polybutadiene and the like, but allyl-type compounds typified by triallyl isocyanurate and triallyl cyanurate are most preferable. Preferably, the blending amount is usually 2 from the viewpoint of both improvement of crosslinking degree and saturation of effect.
-5 parts by weight, preferably 3-5 parts by weight.

An inorganic filler is used as a chemical reaction inhibitor between the crosslinking aid and the resin and rubber components during extrusion molding. As the inorganic filler, talc, clay,
Examples thereof include anhydrous silicic acid, calcium carbonate, calcium silicate and the like, and anhydrous silicic acid, calcium carbonate and calcium silicate are preferable because they do not significantly lower the tensile properties even if they are mixed in a large amount.

Particularly, calcium carbonate having a particle size in the range of 1 to 3 μm suppresses the occurrence of foaming during extrusion molding, is effective in preventing sagging of the tube during tube molding and improving the inner surface tackiness, and is usually 10 to 50. Parts by weight, preferably 20-30
Parts by weight.

Further, in addition to the above components, addition of rare earth oxides for improving the crosslinking efficiency, stabilizers, pigments, antioxidants,
Various additives such as lubricants can be blended.

[0024]

The present invention will be described in more detail with reference to the following examples. Tetrafluoroethylene and α-C2-4
The polymer shown in Table 1 was blended in parts by weight shown in Table 1 with a being a copolymer of olefins (excluding ethylene), b being a copolymer of tetrafluoroethylene and ethylene, and B being a fluorine-based thermoplastic elastomer. Then, 5 parts by weight of triallyl isocyanurate as a cross-linking agent, 30 parts by weight of calcium carbonate as an inorganic filler, and 1 part by weight of sodium stearate as a cross-linking aid were added, and a kneader was used to add 25 parts by weight.
Melt and knead at 0 ° C.

[0025]

[Table 1]

This compound was heated at a die temperature of 250 ° C.
A 40 mm extruder (L / L) set to a head temperature of 250 ° C, a cylinder 1 temperature of 200 ° C, and a cylinder 2 temperature of 250 ° C.
D = 22) was used to extrude into a tube having an inner diameter of 2.0 mm and a wall thickness of 0.5 mm.

Next, Co with a holding capacity of 1 million Curie
^It was crosslinked by irradiating with 10 Mrad of γ-ray using a ^60- ray source. After heating the tube in a heating furnace at 150 ° C., internal pressure was applied in an outer diameter control die so that the inner diameter became 3 mm, and after cooling, a heat shrinkable tube was formed.

In Comparative Examples 1 and 2, the kneader was kneaded at 100 ° C. and the extrusion temperature was set to 100 ° C.
In Comparative Example 3, after melt-kneading with a kneader at 250 ° C., the die temperature was 280 ° C., the head temperature was 280 ° C., the cylinder 1 temperature was 260 ° C., the cylinder 2 temperature was 270 ° C., and the subsequent conditions were the same as above. A heat shrink tube was obtained.

The heat-shrinkable tube produced as described above was placed in a thermostatic chamber at 180 ° C. for 5 minutes to shrink, and then the permanent elongation, brittle fracture resistance, inner surface tackiness, heat resistance, and oil resistance were measured. These measuring methods are as follows.

(1) Permanent elongation: According to JIS K 6301, the heat shrinkable tube has an elongation of 150% in about 15 seconds.
After 10 minutes of holding, the sample is abruptly contracted without being repelled, and after 10 minutes, measurement is performed.

The point at which the elongation rate is 150% is the point at which the marked line length is 1.5 times as long as before being stretched, and the permanent elongation is calculated by Equation 1. Do the same test twice,
Give the average value. PS in Equation 1 is permanent elongation (%), Lo
Is the distance between the marked lines (mm), and l ₁ is the length between the marked lines (mm) after shrinking and leaving for a specified time. Here, the permanent elongation is 20%
In the following, ◯, and those exceeding 20% are marked with x.

[0032]

[Equation 1]

(2) Brittleness and fracture resistance: The heat-shrinkable tube is wound around an iron rod having a diameter of 20 mm and left in an oven at 100 ° C. for a whole day and night. After taking out, the presence or absence of cracks on the tube surface is confirmed, and if there are no cracks or cracks, it is marked with O, and if cracks or cracks occur, it is marked with X.

(3) Tackiness of inner surface: 5 cm of the tube
Cut into lengths, put an iron rod with a diameter of 10 mm on this central part, put a load on this iron rod, and make the total weight of the iron rod and the load 1
kg and keep in this state for 1 minute. After 1 minute, the load is removed and the restorability of the tube is observed. If the sticking of the inner surfaces of the tubes disappears within 15 seconds, the result is ◯, and if it exceeds 15 seconds, the result is x.

(4) Heat resistance: The tube was heated at 250 ° C. for 9 minutes.
When the residual rate after standing in the oven for 6 hours is 80% or more in both tensile strength and elongation as compared with the initial values, it is marked with ◯, and less than 80% is marked with x. At this time, the initial value is JI
According to SK 6301, the sample was pulled at a pulling speed of 500 mm / min, and the results are shown in Table 1. Here, the tensile strength is 1.5k
A general required value is g / mm ² or more.

(5) Oil resistance: If the residual rate after immersion of the tube in JIS No. 2 oil at 120 ° C. for 18 hours is 80% or more of both tensile strength and elongation as compared with the initial values, it is evaluated as ◯ and 80%.
Less than x.

In each of Examples 1 to 7 within the scope of the present invention, tensile strength, elongation, permanent elongation, brittle fracture resistance, inner surface tackiness, heat resistance and oil resistance have sufficient characteristics. In Comparative Examples 1 and 2, neither the fluorine-based resin nor the fluorine-based thermoplastic elastomer was blended, and the tensile strength did not reach the general required value of 1.5 kg / mm ² .

Comparative Example 3 was prepared by mixing only a fluorine-based resin, was inferior in permanent elongation, and did not show rubber elasticity because it was a resin. In Comparative Example 4, the content of the fluorine-based thermoplastic elastomer was 3 parts by weight, which was less than the specified value of the present invention, and the permanent elongation was not improved. On the contrary, in Comparative Example 5,
The content of the fluorine-based thermoplastic elastomer is 60 parts by weight, which exceeds the specified value of the present invention, and the inner surface tackiness, heat resistance,
Oil resistance does not meet the requirements.

Comparative Example 6 is composed of only a fluorine-based elastomer and a fluorine-based resin, and does not contain a fluorine-based thermoplastic elastomer, so that the permanent elongation is not improved. Comparative Examples 7 and 10 are compounds in which only a fluorine-based resin and a fluorine-based thermoplastic elastomer are blended, and Comparative Example 7 lacks elasticity, so that the permanent elongation is not improved. On the contrary, in Comparative Example 10, the internal tack, heat resistance and oil resistance do not satisfy the requirements.

Comparative Example 8 is a product in which only a fluorine-based elastomer and a fluorine-based thermoplastic elastomer are blended, and the inner surface tackiness and tensile strength do not satisfy the requirements. Further, in the composition composed of only the fluorine-based thermoplastic elastomer as in Comparative Example 9, the decrease in the tensile strength and the internal tack were observed as in the case where the content of the fluorine-based thermoplastic elastomer was more than the specified value of the present invention. Adversely affects heat resistance and oil resistance.

[0041]

INDUSTRIAL APPLICABILITY The present invention relates to a copolymer of tetrafluoroethylene and an α-olefin having 2 to 4 carbon atoms (excluding ethylene), and a composition containing the copolymer of tetrafluoroethylene and ethylene. A heat-shrinkable tube composition in which an insulating layer made of a composition containing an inorganic filler and a cross-linking auxiliary agent is crosslinked by irradiation with a composition made of a fluorine-based thermoplastic elastomer containing a fluorine-based elastomer component. It is possible to obtain a heat-shrinkable tube which is excellent in permanent elongation, brittle fracture resistance, inner surface tackiness, heat resistance, oil resistance, and mechanical strength.

It can be easily inferred that if a conductor is coated with this composition, an insulated wire excellent in both of the above can be obtained.

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Claims (2)

[Claims] 1. A composition containing (A) a copolymer of tetrafluoroethylene and an α-olefin having 2 to 4 carbon atoms (excluding ethylene) and a copolymer of tetrafluoroethylene and ethylene, (B) a fluorine-based thermoplastic elastomer containing a fluorine elastomer component:
A heat-shrinkable electrically insulating tube, which is composed of a mixture compounded in a weight ratio of 5 to 50:50 and is crosslinked by irradiation with radiation. 2. The composition comprises 10 to 100 parts by weight.
The heat-shrinkable electrically insulating tube according to claim 1, containing 50 parts by weight of an inorganic filler.