Development of high voltage lead wires using electron beam irradiation

Rudior

Pergamon

Phi

0969~806X(95)00301-0

\. Chcm.

Vol

Flsev~er

Science

46,

No.

J-h.

Ltd

Printed

pp. Y54-YhZ,

in Great

lYY5

Britain

DEVELOPMENT OF HIGH VOLT4GELE.4DVilRESLISING ELECTROEBE451IRRAD14TION Bae Hun-Jai,

Sohn

Ho-Soung

GoldStar Yoido

Cable P.O.Box

and Co.,

580

Seoul,

Choi

Dow-Jung

Ltd. KOREA

ABSTRACT It is known to those skilled to the art that the electric wires used in high voltage operating electric equipments such as TV sets, microwave ovens, duplicators and etc., have such a structure that a conductor is coated with an insulating layer which is encapsulated with a protecting jacket layer. The electric wire specification such as UL and CSA requires superior cut-through property and flame-retardant property of the wire for utilization safety. The cut-through property of insulation material, for example, high density polyethylene, can be increased by crosslinking of the polymer. Also the flame-retardant property of jacket material which protects the flammable inner insulation can be raised by flame-retardant formulating of the material. In the wire and cable industry, crosslinking by electron beam processing is more effective than that by chemical processing in the viewpint of throughput rate of the products, The jacket layer of the wire plays the role of protecting the insulation material from burning. The protecting ability of the jacket is related to its inherent flammability and formability of swollen carbonated layer when burned. Crosslinking of the material gives a good formability of swollen carbonated layer, and it protects the insulation material from direct flame. In formulating the flame-retardant jacket material, a crosslinking system must be considered with base polymers and other flame-retardant additives.

1. Requirements Table

of High

1. The major

C’oltage

characterlsrics

Lead

Wires

of high

voltage

lead

wires

High voltage appliance wiring material in TV receivers is made in use accordance with LL Subject 758 and CSA C 2’2.2 Vo. 16. The conductor shall be of tinned, annealed solid copper wires. The insulation shall be appl ied concentrically over the conductor with cross1 inked polyethylene, The jacket shall be of flame-retardant crosslinked polymeric material and be applied concentrically over the insulation. The major characteristics of wires shall be given in the Table 1.

960 2. Experimental High voltage lead wire utilization safety, Hi& In choosing the materials been considered. 1) Selection

of

2) Formulating protecting

polyethylene

to satisfy

the flame retardant the insulation material

Considering these items, on an industrial scale.

2.1

requires superior cut through property voltage lead uire also requires superior for insulation and jacket by irradiation,

The material

for

we developed

the jacket from

cut

through

material. burning.

irradiated

property The

high

and flame-retardant property for thermal and mechanical properties. the subjects mentioned below have

and dielectric

jacket

voltage

layer

lead

wires

of

withstand the

wire

and put

voltage. plays

them

into

a role

of

production

insulation

For solving the cut through property, the selection of the insulation material is very important. Fundamental studies of various PE(Polyethylenei in relation to irradiation crosslinking have been carried out before practical extruding studies to be undertaken. Three kinds of PE sheets (thickness namly LDPE. MDPE and HDPE have been crosslinked by irradiation, and then, gained is lmm), approximately 75% crosslinking degree. In an effort conducted. are lower MDPE have that they

to make up the determining of the thermal resistant performance, TM studies have been The onset temperature of penetration of LDPE and MDPE are observed at 93°C and 103”C, which than 105”C, nevertheless, HDPE shows 114’C, which is higher than 105°C. In addition, LDPE and been penetrated under the surface balance at 105°C. Therefore, LDPE and MDPE are appeared can not satisfy the cut-through property even though they have high crosslinking degree. However, HDPE shows small penetration at the temperature of higher than 105’C. ‘ENETRATION OF CAOSSLINKED HOPE lO’C/min. Applied force: O.BN ,iccordingly, various kinds of HDPE have been crosslinked by irradiation, and then, TM studies also have been conducted(Fig.1) The onset temperature of penetration of four samples show higher than 105°C. However, three specimens(@@@) have been penetrated under the surface balance at the Density: 0.940-0.943 temperature of higher than 105’C, nevertheless, only one specimen( 0) shows small penetration at the same 0: 0.75 temperature. These results @: 0.B suggest that thermal shock property of HDPE 70 90 110 130 160 are mainly depend upon the degree of Temperature (“Cl plymerization. From these TMA studies, HDPE @ has been chosen for Fig. 1 Onset temperature and penetration of various insulation material of high voltage crosslinked high density polyethylenes. lead uzire.

2.2

Formulating

To overcome flame-retardant deteriorate flame-retardancy

the the the

flame

retardant

combustible property f i 1 lers or the 1 ike insulation resistance to them.

jacket

material

of insulation(polyethylene). are added. The addition property of the polymers

of

in general, such additives. in spite of giving

additives such however, causes an improvement

as to of

9111 International

Mrctlng

on Radiation

961

Processing

In an effort to make up for the deficient property of flammability of the polymers, a material for a layer which can protect the flammable insulating layer is made to have an excellent property of crosslinked polyvinylchloride or crosslinked flame-retardant flame-retardancy. Polyvinylchloride, polyethylene has been chiefly used for a conventional jacket layer. When they have high their mechanical properties and flexibility are deteriorated, therefore, the wire flame-retardency. equipments. In fact, the jacket sheathed ri th them is unsatisfactory to be applied to the electric layer of insulated wire is not necessarily to have high insulation resistance. It is preferable to minimize deterioration of flexibility as much as possible when the material for jacket layer is made to have an excellent property of flameretardancy. The above mentioned conventional materials for jacket layer have an excellent property of flameretardsncy and yet, do not show good flexibility. jacket

For

solving the problems stated above, we have recognized that there exists suitable material that is of being applied for that is suitable for high voltage-operating equipment. Accordingly, in one aspect of the research, there is provided a resin composition that has good flexibility and flame-retardancy, simultaneously. In another aspect of the research, there is provided the insulated wire having jacket layer of the composition. The flame-retardant resin composition according to the problem comprises ethylenevinylacetate-vinylchloride graft copolymer (hereinafter “EVA-K”) as a base component, which itself has fundamental flexibility and a property of flameretardancy, as well as a good filler-loading property. capable

In addition, EV4 VC generate the decomposed gas at burning, A foamed carbonated layer plays a role of a protection wall which is capable of preventing a flammable insulator encapsulated thereby from being directly exposed to a flame, so that a jacket layer of EVA-VC is able to prevent burning. In order to an additional method may be sought in which improve flame-retardant property to EVA-VC polymer, flame-retardant fillers are added to EVA-VC. Flexibility and a property of flameretardancy of EVA-VC is determined by the contents of ethylenevinylacetate and vinylchloride. In general, the higher the content of ethylenevinylacetate is, the more flexible EVA-VC is. On the other hand, the higher the content of vinylchloride is, the better the property of flameretardancy is, However, the quantity of vinylchlorides lowers the flexibility of EVA-VC. Therefore, it is important to select a proper EVA-VC in which the content ratio of ethylenevinylacetate and vinylchloride is such that EV4-VC is excellent in a property of flameretardancy and flexibility, simultaneously. The resin composition according to the problem as a base component in combination with antioxidants. flame retardant fillers, lubricants The test content,

results show while the oxgen

In addition, compound are

the results varied with

that the index of

is a flameretardant composition chlorinated polyethylene(CPE), and monomers with multifunctional

thermal stability of the compound increases

show that the the Sbz03 content

properties of the

the with

compound increasing

of flameretardancy compound.

The thermal stability and the oxgen index increase with to saturate about 8PHR Sbz07 content of the compound. varying with Sb203 content of the compound. The results with increasing Sbz03 content, while the tensile strength

that comprises EVA-VC thermal stabilizers, group.

decreases with CPE content. and

thermal

increasing

stability

CPE

of

the

increasing Sbz03 content, and have a tendency Also, the mechanical property was conducted show that the elongation property decreases shows no change.

Metal hydrate contributes to an effect of flame retardancy when the metal hydrate is burned in a flame, the hydrated water is vaporized to absorb the energy of the flame. Zinc borate is known to provide an synergistic effect of flame retardancy when used in combination with antimony trioxide, and to prohibit the generation of gas when burned. Such a flameretardant fillers not only provide an improvement of the property of flameretardancy but also support the carbonated layer of EVA-VC in order not to collapse. .Also, found used.

the minimum to be smaller

dosage of lrradlation by as much as compared

required with

for the

the yield case when

no

of gel fraction crosslinking

is agent

962

Bae Hun-Jai

et al.

As the monomer with nul ti functional group used in the research there may be employed bi functional group, or trifunctional group, preferably monomer with trifunctional trimethylolpropanetrimethacrylate(TMPT), triallylisocynurate and etc.. The results show that the The relevant experiments were performed. increases with increasing TMPT content, and has a tendency to saturate amount of 3 PHR of the compound.

a monomer with group, such as gel fraction about at the

In accordance with the problem, there is provided flame-retardant composition, essentially consists of 100 weight parts of EVA-VC. 40 to 70 weight parts of chlorinated polyethylene, 40 to 60 weight parts of flame-retardant fillers and 5 to 10 weight parts of monomers with multifunctional group. The EVA-VC used in the study is preferably selected to have 25 to 50% of vinylchloride by weight. Chlorinated polyethylene is preferable in the chlorine content of 25 to 45% by weight, and both crystalline and amorphous types are possible to employ. Chlorinated polyethylene reinforces a mechanical strength and the property of flameretardancy and improves an adhesion to polyethylene insulator. Flame-retardant fillers preferably comprise 10 to 20 weight parts of antimony trioxide, 50 to 80 weight parts of metal hydroxides such as aluminum hydroxide, wesium hydroxide and etc., and 20 to 30 weight parts of zinc borate and may comprise clay, calcium carbonate, barium sulfate and etc..

2.3

Radiation

Sources

We, Gold Star Cable Co., Ltd have three highpower electron beam accelerators, such 750 Kv, 1000 Kv and 1500 Kv. All of them have multiple pass irradiation systems are designed for random twisting of the wire passing through the system to contribute to making dose more uniform throughout the products. The selection of accelerator depends upon the thickness of insulation and jacket of wires.

2.4

Practicability

As mentioned Manufactured requirements

3.

of above, electron of UL

Electron

Beam

Crosslinked

High

Voltage

a detailed description was made for beam crosslinked high voltage lead Subject 758 and CSA C 22.2 No. 16.

Lead

as and

Wires

advantageously wires sufficiently

carrying meet

out. the

Conclusion

High voltage appliance wires for use in TV receivers, microwave ovens, duplicators and etc. are developed in accordance with UL Subject 758 and CSA C 22.2 No. 16. The insulation material has been selected from the investigation of thermal analysis technology and suitable crosslinking condition by electron beam accelerator. From TMA study, one of the most important item, such as high voltage cut-through property has been sufficiently solved. Flammability of wires has been solved by formulating the excellent flame-retardancy jacket material with suitable crosslinking condition. Also, jacket material has been considered in the viewpoint of excellent property of flame-retadancy and flexibility. For solving these points of views, EVA-VC and CPE have been selected as base polymer. 41~0, flame-retardant, filler, stabilizer, crosslinking agents and etc. have been totally investigated. It is quite clear that the newly developed electron beam irradiated crosslinked high voltage lead wires are highly reliable as internal wires for TV sets, microwave ovens, duplicators and etc. It has been proved that they have been adopted by Korean and European famous TV set manufacturers.