WO2011102581A1

WO2011102581A1 - Highly flame-retardant polymer composition for electrical wire and electrical wire produced therewith

Info

Publication number: WO2011102581A1
Application number: PCT/KR2010/006541
Authority: WO
Inventors: Gi-Joon Nam; Won-Jung Kim; Whan-Ki Kim
Original assignee: Ls Cable Ltd.
Priority date: 2010-02-17
Filing date: 2010-09-27
Publication date: 2011-08-25
Also published as: KR20110094697A; KR101601286B1

Abstract

Provided are a flame-retardant insulation composition and an electrical wire produced therewith, which have an excellent balance between heat resistance, mechanical properties and flame retardancy. The flame-retardant insulation composition comprises 50 to 200 parts by weight of halogen-free inorganic flame retardant; 0.2 to 10 parts by weight of a lubricant; 0.2 to 10 parts by weight of a stabilizer, per 100 parts by weight of a base resin including 50 to 90 weight% of ethylene vinyl acetate copolymer singularly or a mixture of ethylene vinyl acetate copolymer and polarized poly olefin, and 10 to 50 weight% of modified polypheny lene oxide, wherein the modified polypheny lene oxide is a mixture including 10 to 50 weight% of polyphenylene oxide and 50 to 90 weight% of at least one rubber selected from the group consisting of high impact polystyrene and styrene-ethylene-butyrene-styrene (SEBS) rubber.

Description

HIGHLY FLAME-RETARDANT POLYMER COMPOSITION FOR ELECTRICAL WIRE AND ELECTRICAL WIRE PRODUCED THEREWITH

The present invention relates to a flame-retardant insulation material and an insulated electrical wire produced therewith. More particularly, the present invention relates to a halogen-free ethylene vinyl acetate-based insulation material.

<Cross-Reference to Related Application>

This application claims priority to Korean Patent Application No. 10-2010-0014253 filed in Republic of Korea on February 17, 2010, the entire contents of which are incorporated herein by reference.

Poly vinyl chloride (PVC) or polyolefin containing a halogenated flame retardant has been widely used as a flame-retardant material for an insulation of an electrical wire because of its excellent mechanical properties and low price. However, halogen-containing compound such as PVC or a halogen-based flame retardant emits toxic gas such as dioxine when it burns, and for this reason, recently restriction against the use of a halogen-based flame-retardant insulation material such as PVC is reinforced for environment protection. And, as an alternative of a halogen-based flame-retardant insulation material, a mixture of halogen-free polyolefin and a metal hydroxide-based inorganic flame retardant is suggested. However, in this case, a metal hydroxide component has a limited thermal stability at the processing temperature, which results in rapid deterioration in mechanical properties. Furthermore, to prevent deterioration in flame retardant properties caused by use of metal hydroxide, because an excessive amount of fillers are required, a polymer resin containing the fillers has an increased viscosity and a decreased processability. Since there is a high possibility that electrical wires for electronic appliances are exposed to heat, the electrical wires should have heat resistance, but for this purpose, if a polyolefin composition containing a large quantity of metal hydroxide is subject to electron beam crosslinking, flame retardant characteristics are remarkably reduced.

Therefore, studies should be steadily made on development of a halogen-free flame-retardant resin composition with sufficient flame retardancy, good mechanical properties and processability, and high economical efficiency.

Therefore, it is an object of the present invention to develop a halogen-free, crosslinked, highly flame-retardant insulation material with excellent mechanical properties such as flexibility and elongation, and excellent processability.

To achieve this object, the present invention provides a flame-retardant insulation material, comprising: a base resin including 50 to 90 weight% of ethylene vinyl acetate copolymer singularly or a mixture of ethylene vinyl acetate copolymer and polarized polyolefin, and 10 to 50 weight% of modified polyphenylene oxide; 50 to 200 parts by weight of an inorganic flame retardant; 0.2 to 10 parts by weight of a lubricant; and 0.2 to 10 parts by weight of a stabilizer, per 100 parts by weight of the base resin. Here, the modified polyphenylene oxide is a mixture including 10 to 50 weight% of polyphenylene oxide and 50 to 90 weight% of at least one rubber selected from the group consisting of high impact polystyrene and styrene-ethylene-butyrene-styrene (SEBS) rubber. And, the inorganic flame retardant is preferably aluminum hydroxide or magnesium hydroxide coated with vinyl silane, fatty acid, aminopolysiloxane or other polymers.

And, the present invention provides an insulated electrical wire with an insulation formed using such flame-retardant insulation material.

An electrical wire obtained using a flame-retardant insulation material of the present invention has excellent flame retardancy, for example, a vertical flame retardancy according to UL 1581 standard and excellent mechanical properties. And, it has good heat resistance and can be used for an insulation of an environmental-friendly, crosslinked electrical wire for electronic appliances.

Hereinafter, the present invention will be described in detail. A flame-retardant insulation material of the present invention comprises a base resin including ethylene vinyl acetate (EVA) copolymer, polyphenylene oxide (PPO) and rubber resin, and a lubricant and a stabilizer, and it has a flame retardant effect without a separate flame retardant.

The EVA copolymer is free of a halogen component and environmentally friendly, and has better flame retardancy than non-polarized polyolefin. However, with the EVA resin singularly, it is difficult to achieve the mechanical strength and elongation required for an insulation for an electrical wire, and it needs a large quantity of halogen-free metal hydroxide to meet the flame retardant standard. In this case, deterioration in mechanical properties inevitably occurs. The inventors of the present invention discovered that a mixture of EVA copolymer, polyphenylene oxide and rubber resin leads to an improvement in mechanical properties and a reduction in usage amount of a flame retardant up to the flame retardant standard, and completed this invention.

PPO polymer such as poly(2,6-dimethylphenylene oxide) is apt to form char, and consequently, has good flame retardancy itself, and it has advantages of high mechanical strength and heat resistance. However, it disadvantageously has brittleness and is difficult to process. Accordingly, if PPO polymer of good flame retardancy is mixed with other polymer, it may produce an insulation material with excellent processability as well as excellent mechanical properties without the need of a crosslinking process, which is favorable to an insulation of an electrical wire.

The present invention uses a mixture of EVA copolymer and modified PPO containing rubber resin to obtain an electrical wire for electronic appliances with excellent flame retardancy, mechanical strength and heat resistance. In the insulation material of the present invention, the base resin comprises 50 to 90 weight% of EVA copolymer and 10 to 50 weight% of modified PPO.

The EVA copolymer usable in the present invention may be a typical EVA copolymer in the art, more preferably a polymer obtained by polymerizing ethylene and vinyl acetate monomer such that the vinyl acetate monomer occupies 10 to 40 weight% of the total weight of the resulting polymer, and the EVA copolymer preferably has a melt flow index between 0.1 and 10g/10 minutes.

If the content of the vinyl acetate monomer is less than 10 weight% in the polymerization, it is not preferable because the amount of used flame retardant is reduced, and if the content of the vinyl acetate monomer exceeds 40 weight%, it is not preferable because the mechanical strength is not maintained. Meanwhile, if the melt flow index of the EVA copolymer is less than 0.1g/10 minutes, it is not preferable because a load increases during extrusion, unfavorably affecting processability, and if the melt flow index of the EVA copolymer exceeds 10g/10 minutes, it is not preferable because sagging occurs during extrusion, making it difficult to handle.

In the insulation material of the present invention, the base resin comprises 50 to 90 weight% of EVA copolymer. At this time, the EVA copolymer may contain a small quantity of polarized polyolefin. In the present invention, the polarized polyolefin means introduction of polar functional groups to untreated polyolefin. In the present invention, the polarized polyolefin is chemically or physically bonded to an inorganic flame retardant with polarity to favorably maintain the mechanical properties of an insulation material.

Polyolefin to be polarized may include polyethylene, low-density polyethylene, linear low-density polyethylene, high-density polyethylene, polypropylene, ethylene-propylene copolymer, ethylene-1-octene copolymer, ethylene-1-butene copolymer, alphaolefin-ethylene block copolymer having 3 to 15 carbon atoms, alphaolefin-ethylene random copolymer having 3 to 15 carbon atoms, ethylene vinyl acetate copolymer with 2 to 40% of vinyl acetate content, ethylene ethyl acrylate copolymer with 2 to 40% of ethyl acrylate content, and so on.

For the purpose of polarization, introduction of functional groups to unmodified polyolefin may be made by treating an unmodified polyolefin with, for example, anhydrous maleic acid, maleic anhydride or glycidyl methacrylate. For example, it is possible to introduce carboxyl groups or carboxylic acid anhydride to polyolefin chains by grafting maleic anhydride onto unmodified polyolefin. This polarization treatment of polyolefin is well known in the art, and its detailed description is omitted herein. In brief, this treatment (for example, grafting) is preferably made on the basis of 0.1 to 5 parts by weight of a polar functional groups-introducing material (for example, maleic anhydride) per 100 parts by weight of polyolefin.

In the case that EVA copolymer and polarized polyolefin are mixed with modified PPO in the base resin, a mixing ratio of the EVA copolymer and the polarized polyolefin is preferably in the range between 50:50 and 95:5 on the basis of weight. When the mixing ratio is in this range, a proper bond strength between the resin and a flame retardant enables maintenance of mechanical properties.

Preferably, the polarized polyolefin used in the base resin of the present invention has a melt flow index between 0.1 and 10, which ensures both mechanical properties and processing characteristics.

Preferably, polyphenylene oxide usable in the present invention is not limited to, including polyphenylene oxide-based polymer typically used in the art, such as poly(2,6-dimethylphenylene oxide).

The term "modified PPO" means a mixture of polyphenylene oxide and rubber resin (elastomer) in the present invention. Modified PPO products consisted of polyphenylene oxide and rubber resin have been available on the market in the art. It is possible to use such PPO products available on the market to the base resin in the present invention. The rubber resin component included in the modified PPO may be, for example, high impact polystyrene (HIPS), styrene-ethylene-butyrene-styrene (SEBS) rubber, polyethylene elastomer and so on. More preferably, the rubber resin component may be, for example, HIPS, SEBS rubber, and their mixtures. Mixing polyphenylene oxide with HIPS and/or SEBS rubber may improve flexibility and elongation of an insulation material.

The present invention is not limited to a specific kind of HIPS and/or SEBS rubber, but may use a typical kind of HIPS and/or SEBS rubber in the art. Here, the HIPS preferably has a styrene content between 30 and 70 weight% on the basis of weight percentage, and its preferred melt flow index is between 0.1 and 30 (190℃, 2.16kg, 10 minutes). And, the SEBS rubber preferably has a styrene content between 30 and 70 weight% on the basis of weight percentage, and its preferred melt flow index is between 0.1 and 30 (190℃, 2.16kg, 10 minutes).

In the insulation material of the present invention, as the modified PPO is used a mixture of 10 to 50 weight% of polyphenylene oxide and 50 to 90 weight% of rubber resin, for example, HIPS and/or SEBS rubber. This content range of polyphenylene oxide and rubber resin advantageously allows a proper mechanical strength, flexibility and processibility as a material for an electrical wire. However, if the content of the polyphenylene oxide in the modified PPO is less than 10 weight%, it is not preferable because there is a reduction in mechanical strength and flame retardant characteristics, resulting in an improper material for an electrical wire, and if the content of the polyphenylene oxide exceeds 50 weight%, it is not preferable because deterioration in flexibility and processibility makes it difficult to use.

The base resin in the insulation material of the present invention includes 10 to 50 weight% of the modified PPO and 50 to 90 weight% of EVA copolymer (containing polarized polyolefin). This content range of the modified PPO in the base resin allows improvement in heat resistance, mechanical strength and flame retardancy, and furthermore, maintains elongation and flexibility of an insulation material to a high level. If the content of the modified PPO in the base resin is less than 10 weight%, it is not preferable because flame retardancy becomes poor, and if the content of the modified PPO in the base resin exceeds 50 weight%, it is not preferable because processibility is deteriorated.

The halogen-free flame-retardant insulation material according to the present invention comprises 50 to 200 parts by weight of an inorganic flame retardant. A preferred inorganic flame retardant may be, for example, aluminum hydroxide or magnesium hydroxide. The flame-retardant insulation material of the present invention basically contains ethylene vinyl acetate copolymer, and also contains polyphenylene oxide with excellent flame retardancy, and accordingly, it effectively ensures a target flame retardancy with a smaller amount of an inorganic flame retardant than a conventional insulation material. And, it leads to improvement in mechanical performance. The present invention may coat the surface of the inorganic flame retardant with an organic material to enhance processing characteristics and assist more uniform dispersion in an organic polymer. For example, it is preferred to coat the surface of aluminum hydroxide or magnesium hydroxide with vinyl silane, fatty acid, aminopolysiloxane or other polymers.

In addition to the inorganic flame retardant, the insulation material of the present invention may further comprise a secondary flame retardant. The secondary flame retardant may be, for example, antimony trioxide, antimony pentoxide, melaminecyanurate or their mixtures. The use of a proper amount of secondary flame retardant in the flame-retardant insulation material allows reduction in usage amount of a metal hydroxide flame retardant that adversely affects the mechanical properties and achieves a desired level of flame retardant effect. The amount of secondary flame retardant may be freely adjusted by an ordinary person skilled in the art depending on target flame retardant level and mechanical properties of the insulation material, and its method is well known in the art and its detailed description is omitted herein.

Besides the above-mentioned base resin and flame retardant, the insulation material of the present invention further comprises a lubricant and a stabilizer. The lubricant can increase releasability of the insulation material from a metal of the surface of a machine, and suppresses generation of frictional heat. The present invention is not limited to a specific kind of lubricant, but may use a typical kind of lubricant in the art. For example, the lubicant may be low molecular weight polyethylene, stearic acid, stearyl alcohol, butyl stearate, wax and so on. A preferred content of the lubricant is 0.2 to 10 parts by weight per 100 parts by weight of the base resin. If the content of the lubricant is less than 0.2 parts by weight, it is not preferable because a lubrication effect is insufficient, and if the content of the lubricant exceeds 10 parts by weight, it is not preferable because there is deterioration in the entire properties of the resin composition, such as poor mixing.

In the present invention, the stabilizer may be an antioxidant. The antioxidant prevents air oxidation of a polymer resin that may occur at high temperature. Preferably, the antioxidant of the present invention may be any one selected from the group consisting of thioesters and phenols, or mixtures thereof, and more preferably, for example, A/O 1010. In the present invention, the content of the antioxidant is 0.2 to 10 parts by weight per 100 parts by weight of the base resin. If the content of the antioxidant is less than 0.2 parts by weight, it is not preferable because an antioxidant effect is insufficient, and if the content of the antioxidant exceeds 10 parts by weight, it is not preferable because a further antioxidant effect is not obtained. The above-mentioned value is a proper content range of the antioxidant.

Besides the above-mentioned components, the flame-retardant insulation material according to the present invention may further comprise various kinds of functional additives used typically in an insulation resin composition, within the range not hindering the effects of the present invention. For example, the additives may an anti-UV agent, an anti-blocking agent, an antistatic agent, wax, a coupling agent, a pigment and so on, and although not shown in the embodiment, various kinds of materials may be selected and used according to necessity.

Also, the present invention provides an insulated electrical wire with an insulation formed using the flame-retardant insulation material. Due to high temperature stability of polyphenylene oxide, formation of an insulation using the flame-retardant insulation material of the present invention effectively allows crosslinking without sacrifice of flame retardancy. The crosslinking method may be properly determined by an ordinary person skilled in the art, and crosslinking may be performed, for example, by electronic beam radiation. An insulation surrounding a metal conductor may be manufactured by a typical method using the flame-retardant insulation material of the present invention, and the method is well known in the art and its detailed description is omitted herein.

Hereinafter, the present invention will be described in detail through examples. However, the description proposed herein is just a preferable example for the purpose of illustrations only, not intended to limit the scope of the invention, so it should be understood that the examples are provided for a more definite explanation to an ordinary person skilled in the art.

Flame-retardant resin compositions of examples and comparative examples were prepared according to an elemental ratio of the following table 1 in order to find out performance changes depending on components of the flame-retardant insulation composition of the present invention. The unit of Table 1 is parts by weight, and values beyond the elemental ratio of the present invention are indicated in bold italic font.

Table 1

Elemental ratio (parts by weight)	Examples			Comparative examples
Elemental ratio (parts by weight)	1	2	3	1	2	3	4
Ethylene vinyl acetate¹⁾	80	60	50	*100*	80	*100*	80
Polarized polyolefin²⁾	-	10	-	-	20	-	20
Modified polyphenylene oxide³⁾	20	30	50	0	0	0	0
Inorganic flame retardant^†	150	100	80	250	*250*	150	150
Secondary flame retardant^‡	30	-	-	-	-	100	100
Lubricant^*	0.5	0.5	0.5	0.5	0.5	0.5	-
Stabilizer^※	0.5	0.5	0.5	0.5	0.5	0.5	-

[Components of Table 1]

1) EVA180 made by Mitsui. Melt flow index: 0.2g/10min. When polymerizing, 33 weight% of vinyl acetate monomer occupies in a mixture of monomers.

2) Resin obtained by grafting 0.9 weight% of maleic anhydride monomer onto polyethylene. Melt flow index: 2.0g/10min.

3) Xyron WH100 made by Asahi Kasei.

† Kisuma 5P made by Kyowa, magnesium hydroxide surface-coated with silane

‡ Melaminecyanurate

* PE-based Wax product, LC-Wax 102N made by Lion Chem.

※ Antioxidant, Ir-1010 made by Ciba Specialty.

Electrical cable sections were produced in which insulations were formed using compositions of examples 1 through 3 and comparative examples 1 through 4 as follows.

First, an insulation section was manufactured by compound-processing each composition at 160℃ using a 3L kneader and extruding onto a conductor using a 45mm single screw extruder, and an electrical cable section with the insulation that conforms to UL 3691 standard was produced and evaluated. At this time, the electron beam divergence of an electron beam emitter was adjusted to 25 Mrad for crosslinking of the insulation.

The electrical cable sections obtained as mentioned above were tested for mechanical properties, flame retardancy and appearance, and the test results are shown in the following table 2. The test conditions are as follows:

1) Mechanical properties at room temperature

According to UL 1581 standard, electrical cables for electronic appliances should have a tensile strength at room temperature of 1.05 kgf/mm² or higher, and an elongation at room temperature of 150% or higher.

2) Mechanical properties after heating

According to UL 1581 standard, electrical cables for electronic appliances of which heat resistance temperature is 105℃ should have a retention tensile strength of 70% or higher and a retention elongation of 50% or higher, after heating at 136℃ for 168 hours.

3) Flame retardancy

To evaluate the flame retardancy of a highly flame-retardant heat-shrinkable tube, UL 1581 (VW-1) vertical flame test was carried out. Specifically, flaming for 15 seconds and extinguishing for 15 seconds are repeated 5 times, at this time, the total burning time is 60 seconds or less, and a section that was not completely burned is evaluated.

4) Appearance

The surface appearance, including color is observed by naked eyes, and if an electrical wire section has a smooth surface without any protrusion, it is evaluated as having passed the test, and if the electrical wire section has a rough surface with protrusions, it is evaluated as having failed the test.

Table 2

		Examples			Comparative examples
		1	2	3	1	2	3	4
Properties at room temperature	Tensile strength(kgf/mm²)	1.3	1.45	1.9	0.7	0.95	0.85	0.98
Properties at room temperature	Elongation(%)	330	270	215	85	100	98	110
Properties after high temperature aging	Retention tensile strength(%)	86	92	106	104	94	87	85
Properties after high temperature aging	Retention elongation(%)	88	95	102	96	97	85	80
Vertical flame retardancy(VW-1)		pass	pass	pass	fail	fail	pass	pass
Cable appearance		pass	pass	pass	pass	pass	pass	pass

As shown in Table 2, according to the property measurement results, the compositions of examples met all the standards for mechanical properties, vertical flame retardancy, appearance and economical efficiency, under conditions of room temperature and heating. However, the comparative example 1 containing EVA copolymer singularly in a base resin exhibited poor mechanical properties including tensile strength and elongation. In particular, the comparative example 1 used an inorganic flame retardant 2.5 times more than the example 2, but did not meet the flame retardant standard. The comparative example 3 used different amounts of an inorganic flame retardant and a secondary flame retardant from the comparative example 1, but it also exhibited poor mechanical properties and is improper as an insulation material. The comparative examples 2 and 4 contained EVA resin and polarized polyolefin but did not contain modified PPO in a base resin, and they exhibited good properties after heating, but did not meet the standard for mechanical properties at room temperature, and accordingly, they are improper as an insulation material for electronic appliances. From these results, it is found that a flame-retardant insulation material of the present invention and an electrical wire produced therewith have an excellent balance between mechanical properties and flame retardancy.

Hereinabove, the preferred embodiments of the present invention was described in detail. It should be understood that the terms used in the specification and the appended claims should not be construed as limited to general and dictionary meanings, but interpreted based on the meanings and concepts corresponding to technical aspects of the present invention on the basis of the principle that the inventor is allowed to define terms appropriately for the best explanation.

Claims

A flame-retardant insulation composition, comprising:

per 100 parts by weight of a base resin including 50 to 90 weight% of ethylene vinyl acetate copolymer singularly or a mixture of ethylene vinyl acetate copolymer and polarized polyolefin, and 10 to 50 weight% of modified polyphenylene oxide,

50 to 200 parts by weight of a halogen-free inorganic flame retardant;

0.2 to 10 parts by weight of a lubricant; and

0.2 to 10 parts by weight of a stabilizer,

wherein the modified polyphenylene oxide is a mixture including 10 to 50 weight% of polyphenylene oxide and 50 to 90 weight% of at least one rubber selected from the group consisting of high impact polystyrene and styrene-ethylene-butyrene-styrene (SEBS) rubber.
The flame-retardant insulation composition according to claim 1,

wherein a ratio of the ethylene vinyl acetate copolymer and the polarized polyolefin is between 50:50 and 95:5 on the basis of weight percentage.
The flame-retardant insulation composition according to claim 1,

wherein the polarized polyolefin has a melt flow index between 0.1 and 10g/10 minutes.
The flame-retardant insulation composition according to claim 1,

wherein the polarized polyolefin is obtained by treating an unmodified polyolefin with maleic anhydride or glycidyl methacrylate, the unmodified polyolefin being selected from the group consisting of polyethylene, low-density polyethylene, linear low-density polyethylene, high-density polyethylene, polypropylene, ethylene-propylene copolymer, ethylene-1-octene copolymer, ethylene-1-butene copolymer, alphaolefin-ethylene block copolymer having 3 to 15 carbon atoms, alphafolefin-ethylene random copolymer having 3 to 15 carbon atoms, ethylene vinyl acetate copolymer with 2 to 40% of vinyl acetate content, ethylene ethyl acrylate copolymer with 2 to 40% of ethyl acrylate content, and their mixtures.
The flame-retardant insulation composition according to claim 4,

wherein the treating is graft polymerization.
The flame-retardant insulation composition according to claim 1,

wherein the ethylene vinyl acetate copolymer has a melt flow index between 0.1 and 10g/10 minutes, and is obtained by polymerization such that the weight of vinyl acetate monomer occupies between 10 and 40 weight% of the total weight of monomers.
The flame-retardant insulation composition according to claim 1,

wherein the polyphenylene oxide has a melt flow index between 5 and 50 (220℃, 10kg, 10 minutes).
The flame-retardant insulation composition according to claim 1,

wherein the high impact polystyrene has 30 and 70% of styrene on the basis of weight percentage, and a melt flow index between 0.1 and 30 (190℃, 2.16kg, 10 minutes).
The flame-retardant insulation composition according to claim 1,

wherein the styrene-ethylene-butylene-styrene rubber has 30 and 70% of styrene on the basis of weight percentage, and a melt flow index between 0.1 and 30 (190℃, 2.16kg, 10 minutes).
The flame-retardant insulation composition according to claim 1,

wherein the inorganic flame retardant is aluminium hydroxide or magnesium hydroxide coated with vinyl silane, fatty acid, aminopolysiloxane or polymer.
The flame-retardant insulation composition according to claim 1, further comprising:

a secondary flame retardant selected from antimony trioxide, antimony pentoxide, melaminecyanurate or their mixtures.
An insulated electrical wire, comprising:

a conductor; and

an insulation surrounding the conductor,

wherein the insulation is made from the flame-retardant insulation composition defined in any of claims 1 through 11.