WO2005123828A1

WO2005123828A1 - Resin composition resistant to thermal deformation and cut-through and the insulation material and the cable using thereit

Info

Publication number: WO2005123828A1
Application number: PCT/KR2004/001429
Authority: WO
Inventors: Do Hyun Park; Jin Ho Nam
Original assignee: Lg Cable Ltd.
Priority date: 2004-06-15
Filing date: 2004-06-15
Publication date: 2005-12-29
Also published as: CN1969007B; CN1969007A; JP2008501846A

Abstract

The present invention provides a resin composition, which comprises: a base resin comprising ethylene copolymer and ethylene propylene rubber; 10-120 parts by weight, based on 100parts by weight of the base material, of a flame retardant; 5-50 parts by weight of an inorganic additive; and a given crosslinking coagent. The inventive resin composition contains the polymer resins with high crosslinking efficiency, such as low-crystalline ethylene copolymer and ethylene copolymer and ethylene propylene rubber, which may have high crosslinking density even upon exposure to a given amount of electron beam. Thus, after crosslinking, the resin composition shows little or no change in mechanical properties (e.g., reduction in elongation) and in thermal properties. Also, the present invention provides a resin composition having a suitable crosslinking structure to meet thermal deformation resistance at high temperature and cut-through resistance, which are very important in high-voltage cables, as well as an insulation material made of the composition and a cable including the insulation material.

Description

RESIN COMPOSITION RESISTANT TO THERMAL DEFORMATION AND CUT- THROUGH AND THE INSULATION MATERIAL AND THE CABLE USING THERE IT

Technical Field

The present invention relates to a resin composition

excellent in thermal deformation resistance at high temperature

and cut-through resistance, and to an insulation material made

of the composition and a cable including the insulation

material .

As used herein, the term "cut-through" means that an

insulation material for cables gets damaged when the insulation

material is brought into contact with a metal piece having

sharp edges. The cut-through resistance may be measured by,

for example, a method shown in FIG. 1. As used herein, the

term "cut-through resistance" means a property of inhibiting or

preventing the cut-through indicating this damage of the

insulation material .

Background Art

In the prior art, as a resin composition which is used as

an insulation material for cables, polar resins containing chlorine, a halogen atom, have been frequently used. The polar

resins include chlorinated polyethylene, polyvinyl chloride and

the like. Moreover, chlorinated polyethylene is also used in a

combination with a resin of vinyl chloride bound to ethylene

vinyl acrylate.

In the prior art, the content of ethylene copolymer, such

as ethylene vinyl acetate copolymer or ethylene ethyl acrylate

copolymer, was suitably adjusted and used in a combination with

polyethylene, in an attempt to improve physical properties,

such as electrical properties, thermal resistance and thermal

deformation resistance.

The use of the resin composition as described above can

satisfy, to some extent, a flame retardancy which is especially

required in an insulation material for cables. The flame

retardancy of cables for devices generally needs to be

evaluated by performing horizontal and vertical burning tests

by UL (Underwriters Laboratory) standards for finished products.

It is known that, upon burning, halogen-containing resins

generate non-burnable heavy halogen gas and react with

additives so as to form solid ashes, thus inhibiting the

burning of the materials.

The measurement of the flame retardancy can be performed by horizontal burning, vertical burning and plate-type test

methods in UL (Underwriters Laboratory) , as well as an oxygen

index method and an FMVSS (Federal Motor Vehicle Safety

Standards) 302 method.

Since such halogen-containing resin compositions

fundamentally possess flame retardancy, they contain a small

amount of an organic or inorganic flame retardant for improving

flame retardancy. As a result, the fundamental properties of

the resin compositions are maintained, and thus an insulation

material made of such resin compositions shows excellent

electrical and mechanical properties. Also, since the addition

of a small amount of the organic or inorganic flame retardant

does not cause an increase in the viscosity of the insulation

material, the insulation material also has excellent extrusion

processibility.

If various polar resins used in the prior art are used

alone, it will be difficult to meet the property requirements

of an insulation material. However, the halogen-containing

polar resins are physically and chemically compatible with each

other. Thus, there have been attempts to use different polar

resins having different properties together to develop an

insulation material exhibiting excellent intrinsic properties of each of the resins or synergistic effects.

In the prior art, halogen-containing polar resin

compositions, such as chlorinated polyethylene, polyvinyl

chloride, and ethylene vinyl acetate-vinyl chloride, were used

as a base resin. Either insulation materials made of such

resin compositions or ' cables coated with such insulation

materials are crosslinked with electron beam in order to

prevent them from being deformed by a given load at high

temperature and to prevent cut-through.

However, in the process of crosslinking the resin

composition with electron beam, a halogen atom contained in the

resin composition used as a base resin is decomposed. The

insulation material decomposed during the crosslinking process

may show a remarkable reduction in thermal resistance such that

thermal deformation resistance and cut-through resistance canot

be satisfied.

To meet properties against thermal deformation, the resin

composition must have high crosslinking density, and for this

purpose, the resin composition needs to be exposed to an excess

of electron beam. If the crystalline resins with a higher

melting temperature than a given temperature is exposed to an

excess of electron beam, mechanical properties such as elongation will be rapidly reduced, and in the exposure process

of the resin to electron beam, the decomposition of the polymer

resin will be accelerated so that the thermal deformation

resistance of the materials will be remarkably reduced. Thus,

if the materials are exposed to a certain temperature for a

long period of time, it will show low elongation. If general

mechanical properties required for the insulation materials are

considered, an excess of organic or inorganic additives can not

be added to crystalline resins. As a result, the insulation

materials will show low flame retardancy, and also finished

products cannot meet the desired flame retardancy.

Generally, resin compositions which contain suitable

amounts of ethylene copolymer and polyethylene have high

melting point. Crystalline polymers show an increase in the

regularity of molecular arrangement with an increase in

crystallinity so that they have a higher melting point than

that of polymers with low crystallinity. Concrete data on the

crystallinity of polymers and on the melting point of polymers

with crystallinity are shown in the following reference

publications: (1) P. J. Flory, Principles of Polymer Chemistry,

1953; (2) F. W. Billmeye, Textbook of Polymer Science, fourth

ed.; (3) J.F Sharckefold, Introduction to materials science and engineering, Macmillan Publishing Company, 1988; (4) J. D.

Ferry, Viscoelastic Properties of Polymers; (5) P. C. Hiemenz,

Polymer Chemistry-The Basic Concepts. As described above, the resins are very low in the

crosslinking efficiency by electron beam, and also the

evaluation of thermal deformation resistance and cut-through

resistance of resin compositions which are used in wires for

devices is performed at a high temperature of more than 100 °C

around which the crystalline resin compositions are melted.

Also, due to the decomposition of halogen atoms in the

resin composition, the flame retardancy of the insulation

material becomes unstable and there is a difference in flame

retardancy between an insulation material and a cable on

finished products. The insulation material made of the

halogen-containing resin composition show a great variation in

properties depending on crosslinking conditions, which makes it

difficult to establish the crosslinking conditions.

Brief Description of the Drawings

FIG. 1 is a schematic view measuring a cut-through

resistance of the finished cable products according to this invention.

Disclosure of Invention

Therefore, the present invention has been made to solve

the above-described problems occurring in the prior art, and it

is an object of the present invention is to provide a resin

composition which contains polymer resins with high

crosslinking efficiency, such as low-crystalline ethylene

copolymer and ethylene propylene rubber, which can have high

crosslinking density even upon exposure to a given amount of

electron beam. For this reason, after crosslinking, the resin

composition has little or no changes in mechanical properties

(e.g., reduction in elongation) or in thermal properties.

Another object of the present invention is to provide an

insulation material having a suitable crosslinking structure to

meet thermal deformation resistance at high temperature and

cut-through resistance which are very important in high-voltage

cables . To achieve the above objects, the present invention

provides a resin composition comprising: a base resin

comprising ethylene copolymer and ethylene propylene rubber; 10

to 120 parts by weight, based on 100 parts by weight of the base resin, of a flame retardant; 5-50 parts by weight of an

inorganic additive; and a given crosslinking coagent .

The low-crystalline ethylene copolymer in the inventive

resin composition is preferably at least one selected from

ethylene vinyl acetate, ethylene ethyl acrylate, ethylene butyl

acrylate, ethylene butene copolymer, and ethylene octene

copolymer, and the content of ethylene copolymer is preferably

20-80 parts by weight based on 100 parts by weight of the base

resin.

Furthermore, the ethylene copolymer in the inventive

resin composition preferably contains a modified ethylene

copolymer containing a polar group. The modified ethylene

copolymer is preferably at least one selected from ethylene

vinyl acetate, ethylene butyl acrylate and ethylene butyl

copolymers, which contain a maleic anhydride. Also, the

content of the modified ethylene copolymer is preferably 1 to

20 parts by weight based on 100 parts by weight of the base

resin. Also, the ethylene propylene rubber in the inventive

resin composition is preferably at least one selected from

ethylene-propylene bipolymer, and ethylene-propylene-diene

terpolymer. Also, the flame retardant in the inventive resin

composition preferably includes at least one organic flame

retardant selected from halogen, such as bromine or chlorine,

nitrogen and phosphorus, in which the organic flame retardant

is used in an amount of 5-60 parts by weight based on 100 parts

by weight of the base resin. Also, the flame retardant

preferably includes at least one inorganic flame retardant

selected from aluminum tri-hydroxide, magnesium di-hydroxide,

hydrated magnesium calcium carbonate, boron and zinc, in which

the inorganic flame retardant is used in an amount of 5-60

parts by weight based on 100 parts by weight of the base resin.

Also, the inorganic additive in the inventive composition

is preferably at least one selected from talc and clay, and

surface-treated with fatty acid, silane or the like.

Other objects, features and advantages of the present

invention will be more clearly understood from preferred

embodiments according to the following detailed description

taken in conjunction with the accompanying drawing. Hereinafter, the construction of the present invention

will be described in detail with reference to the accompanying

drawing. The present invention provides a resin composition

which is excellent in thermal deformation resistance at high temperature and cut-through resistance and can be crosslinked

by chemical, water or irradiation crosslinking, as well as an

insulation material made of the resin composition and a cable

including the insulation material. To prepare the inventive

base resin among the components of the insulation material,

ethylene copolymer and ethylene-propylene copolymer are used.

As the ethylene copolymer, at least one selected from the

group consisting of ethylene vinyl acetate (EVA) , ethylene

ethyl acrylate (EEA) , ethylene butyl acrylate (EBA) , ethylene

butene copolymer, and ethylene octene copolymer, is used.

To improve the mechanical and thermal properties of the

insulation material in the present invention, the base resin

may contain a modified ethylene copolymer introduced with a

polar group. The modified ethylene copolymer used in the

present invention is at least one selected from the group

consisting of ethylene vinyl acetate, ethylene butyl acrylate

and ethylene butene copolymer, which contain a maleic anhydride.

Examples of the flame retardant for the flame retardancy

of the inventive insulation material include an organic flame

retardant and an inorganic flame retardant. The organic flame

retardant contains halogen, such as bromine or chlorine, or

nitrogen or phosphorus . Examples of the inorganic flame retardant, which can be used in the present invention, include

aluminum tri-hydroxide, magnesium di-hydroxide, hydrated

magnesium calcium carbonate, zinc and boron. This inorganic

flame retardant is surface-treated with fatty acid, silane or

the like.

The inventive insulation material contains the inorganic

additive, such as talc or clay. The inorganic additive is

surface-treated with fatty acid, silane or the like. The

insulation material can be crosslinked by chemical means, water

or irradiation, in order to meet thermal properties and

mechanical properties required in cables. For chemical

crosslinking, organic peroxide is used as a crosslinking agent,

and at least one selected from the group consisting of

trimethylolpropane, trimethacrylate, triallylisocyanurate and

organic peroxide is used as a crosslinking coagent so as to

increase crosslinking density. For water crosslinking, silane,

tin or platinum is added. For irradiation crosslinking, at

least one selected from the group consisting of

trimethylolpropane, trimethacrylate and triallylisocyanurate is

used as a crosslinking coagent .

The present invention provides an insulation material for

cables for high-voltage devices, which is excellent in thermal deformation resistance at high temperature and cut-through

resistance and can be crosslinked by chemical means, water and

irradiation. As the base resin among the components of the insulation

material, ethylene copolymer and ethylene propylene rubber are

used. If necessary, a modified ethylene copolymer may be

additionally used in the base resin.

As the ethylene propylene rubber, ethylene-propylene

bipolymer or ethylene-propylene-diene terpolymer which has an

ethylene content of 40-85 parts by weight is used.

Examples of the ethylene copolymer, which is used in the

present invention, include ethylene vinyl acetate, ethylene

ethyl acrylate, ethylene butyl acrylate, ethylene butene

copolymer, and ethylene octene copolymer. The ethylene

copolymer is used in a combination with the ethylene propylene

rubber in an amount of 20 to 80 parts by weight based on 100

parts by weight of the base resin. The use of the ethylene

copolymer in an amount of less than 20 parts by weight will

cause a reduction in tensile strength and thermal properties,

and an amount of use of more than 80 parts by weight will

result in a remarkable reduction in thermal deformation

resistance at high temperature and does not meet cut-through resistance in cables .

Examples of the modified ethylene copolymer which is used

to improve the mechanical and thermal properties of the

insulation material in the present invention include ethylene

vinyl acetate, ethylene butyl acrylate and ethylene butene

copolymers, which contain a maleic anhydride. The modified

ethylene copolymer is used in an amount of 1 to 20 parts by

weight based on 100 parts by weight of the base resin. If the

modified ethylene copolymer is used in an amount of less than 1

part by weight, the effects of the modified resin on tensile

strength and thermal resistance cannot be expected, and if it

is used in an amount of more than 20 parts by weight, it will

cause a sharp reduction in elongation and an increase in

viscosity, making extrusion processibility poor.

In the present invention, for the flame retardancy of the

insulation material, the organic flame retardant containing

halogen, such as bromine or chlorine, nitrogen or phosphorus,

is used in an amount of 5-60 parts by weight. If the organic

flame retardant is used in an amount of 5 parts by weight, the

flame retardancy of the insulation material cannot be expected,

and at an amount of 60 parts by weight, it will result in

reductions in the tensile strength, elongation and thermal resistance of the insulation material.

In a combination with the organic flame retardant, the

inorganic flame retardant, such as aluminum tri-hydroxide,

magnesium di-hydroxide, hydrated magnesium calcium carbonate,

boron or zinc, is used in an amount of 10-60 parts. If the

inorganic flame retardant is used in less than 10 parts by

weight of the inorganic flame retardant, the insulation

material cannot secure flame retardancy, and if the inorganic

flame retardant is used in more than 60 parts by weight, the

insulation material will show sharp reductions in tensile

strength, thermal resistance and extrusion processibility.

The inventive resin composition can be crosslinked by

water, irradiation or chemical means. For chemical

crosslinking, at least one chemical crosslinking coagent

selected from organic peroxide, trimethylolpropane,

trimethacrylate, triallylisocyanurate and polybutadiene is used

in an amount of 1 to 15 parts by weight . At less than 1 part

by weight of the chemical crosslinking coagent, the insulation

material will have low crosslinking degree, and thus low

tensile strength and thermal resistance. At more than 15 parts

by weight, the crosslinking coagent will cause a shape

reduction in the elongation of the insulation material. For irradiation crosslinking, at least one chemical crosslinking

coagent selected from trimethylolpropane, trimethacrylate,

triallylisocyanurate and polybutadiene is used in an amount of

1 to 5 parts by weight. At less than 1 part by weight, the

tensile strength and thermal resistance of the insulation

material cannot be improved, and at more than 5 parts by weight,

the elongation of the insulation material will be reduced. For

water crosslinking, silane, tin or platinum is used as a water

crosslinking coagent. In the chemical crosslinking, organic

peroxide is used as a crosslinking agent .

In addition to the above-described components, the

inventive resin composition may contain a given amount of

additives, such as antioxidants and talc, which are generally

contained in an insulation material for cables for high-voltage

devices .

The inventive resin composition can have the desired

thermal deformation resistance and cut-through resistance by

crosslinking.

Best Mode for Carrying Out the Invention

Examples Hereinafter, the inventive flame-retardant insulation

material for cables for high-voltage devices, which is

excellent in thermal deformation resistance at high temperature

and cut-through resistance and can be crosslinked by

irradiation, chemical means or water, will be described in

detail by the following examples .

In Examples 1 to 4 according to the present invention,

only ethylene vinyl acetate was contained as ethylene copolymer,

and in Examples 1-6, the base resin consisted of ethylene

propylene rubber and ethylene copolymer. As the inorganic

additive, talc was used, and as the organic flame retardant, a

bromine flame retardant was used. Also, as the inorganic flame

retardant, aluminum tri-hydroxide and magnesium di-hydroxide

were used. Also, as the irradiation crosslinking coagent

rimethylolpropane was used, and as the chemical crosslinking

coagent, organic peroxide was used.

Furthermore, in Examples, given amounts of antioxidants

and talc which are generally contained in an insulation

material for cables for high-voltage devices were used.

Table 1 below shows the components of a resin composition

according to each of Examples . (Table 1)

In Comparative Examples 1 to 5 according to the prior art,

the whole or parts of a base resin in an insulation material

for cables was made of high-density polyethylene or linear low-

density polyethylene which has high melting point and

crystallinity and is hard, or ethylene vinyl acetate, polyvinyl

chloride, polyvinyl chloride, or chlorinated polyethylene. In

view of flame retardancy, polyvinyl chloride, chlorine- containing ethylene vinyl acetate or chlorinated polyethylene

was also used as a flame-retardant material to meet thermal

deformation resistance at high temperature and cut-through

resistance, In Comparative Examples 4 and 5, polyvinyl

chloride and chlorinated polyethylene were used to provide a

halogen element.

Table 2 below shows the components of each of Comparative

Examples according to the prior art .

(Table 2)

The results of comparison of properties between Examples meeting excellent properties and Comparative Example are as

follows. In Examples of the present invention, the bromine

flame retardant, aluminum tri-hydroxide and talc were added to

ethylene propylene rubber and ethylene copolymer. As a result,

thermal deformation at high temperature was remarkably lower in

Examples than that in Comparative Examples, and cut-through

resistance was shown to be unsatisfactory in all Comparative

Examples but satisfactory in all Examples.

Table 3 below shows the comparison of properties between

Examples and Comparative Examples,

(Table 3)

S: Satisfactory

U: Unsatisfactory

The tensile strength and the elongation in Table 3 were

measured according to ASTM (American Society for Testing and Materials) D 638. The thermal deformation was evaluated by

placing a blade-shaped jig on a sample at 105 °C and applying a

load of 450 g onto the jig. The cut-through resistance was

evaluated for finished cable products as shown in FIG. 1. As

shown in FIG. 1, the cut-through resistance was measured by

suspending the inventive finished cable product to a metal

mandrel 1 supported by a metal supporter 2 and applying high

voltage to the cable product through a high-voltage connection

3.

The present invention has been described in further

detail by way of Examples and Comparative Examples. However,

the scope of the present invention is not limited to Examples,

and any person skilled in the art will appreciate that various

modifications, additions and substitutions are possible,

without departing from the scope and spirit of the invention as

disclosed in the accompanying claims.

Industrial Applicability The inventive resin composition comprises a combination

of ethylene copolymer and ethylene propylene rubber, as the

base rein, and also given amounts of the flame retardant, the

inorganic additive and the crosslinking coagent. The inventive resin composition and the insulation material made of the same

may have high crosslinking density even upon exposure to a

given amount of electron beam. After crosslinking, this resin

composition with high crosslinking efficiency shows little or

no changes in mechanical properties (e.g., reduction in

elongation) and in thermal properties. Also, cables including

an insulation layer made of the inventive resin composition can

meet thermal deformation resistance and cut-through resistance

which are very important in high-voltage cables, even when high

voltage is applied to the inventive cables.

Although the preferred embodiments of the present

invention have been disclosed, many other modifications and

variations can be made without departing from the scope and

spirit of the invention. Thus, such modifications and

variations will be within the scope of the present invention as

disclosed in the accompanying claims.

Claims

What Is Claimed Is:

1. A resin composition with thermal deformation

resistance and cut-through resistance, which comprises: a base resin comprising ethylene copolymer and ethylene

propylene rubber;

10-120 parts by weight, based on 100 parts by weight of

the base material, of a flame retardant;

5-50 parts by weight of an inorganic additive; and a crosslinking coagent.

2. The resin composition of Claim 1, wherein the ethylene

copolymer is at least one selected from ethylene vinyl acetate,

ethylene ethyl acrylate, ethylene butyl acrylate, ethylene

butene copolymer, and ethylene octene copolymer.

3. The resin composition of Claim 1, wherein the amount

of the ethylene copolymer is 20-80 parts by weight based on 100

parts by weight of the base resin.

4. The resin composition of Claim 1, wherein the base

resin further comprises a modified ethylene copolymer

containing a polar group.

5. The resin composition of Claim 4, wherein the modified

ethylene copolymer is at least one selected from ethylene vinyl

acetate, ethylene butyl acrylate and ethylene butyl copolymers,

which contain a maleic anhydride.

6. The resin composition of Claim 4, wherein the amount

of the modified ethylene copolymer is 1-20 parts by weight

based on 100 parts by weight of the base resin.

7. The resin composition of Claim 1, wherein the ethylene

propylene rubber is at least one selected from ethylene-

propylene bipolymer and ethylene-propylene-diene terpolymer.

8. The resin composition of Claim 1, wherein the flame

retardant is an organic flame retardant which is used in an

amount of 5-60 parts by weight based on 100 parts of the base

resin.

9. The resin composition of Claim 8, wherein the organic

flame retardant contains at least one selected from halogen,

such as bromine or chlorine, nitrogen and phosphorus.

10. The resin composition of Claim 1, wherein the flame

retardant is an inorganic flame retardant which is used in an

amount of 5-60 parts by weight based on 100 parts by weigh of

the base resin.

11. The resin composition of Claim 10, wherein the

inorganic flame retardant is at least one selected from

aluminum tri-hydroxide, magnesium di-hydroxide, hydrated

magnesium calcium carbonate, boron and zinc.

12. The resin composition of Claim 1, wherein the

inorganic additive is at least one selected from talc and clay,

and surface-treated with fatty acid or silane.

13. The resin composition of Claim 1, wherein the

crosslinking coagent is at least one irradiation crosslinking

coagent selected from trimethylolpropane, trimethacrylate,

triallylisocyanurate and polybutadiene, and is used to

crosslink the resin composition by irradiation.

14. The resin composition of Claim 13, wherein the amount

of the irradiation crosslinking coagent is 1-5 parts by weight.

15. The resin composition of Claim 1, wherein the

crosslinking coagent is at least one chemical crosslinking

coagent selected from organic peroxide, trimethylolpropane,

trimethacrylate, triallylisocyanurate and polybutadiene, and is

used to chemically crosslink the resin composition.

16. The resin composition of Claim 15, wherein the amount

of the chemical crosslinking coagent is 1-15 parts by weight.

17. The resin composition of Claim 1, wherein the

crosslinking coagent is at least water crosslinking coagent

selected from silane, tin and platinum, and is used to water-

crosslink the resin composition.

18. An insulation material made of a resin composition as

set forth in any one of Claims 1 to 17.

19. A cable including an insulation material made of a

resin composition as set forth in any one of Claims 1 to 17.