DD160976A3 - METHOD FOR PRODUCING INSULATION FROM RADIATION-LINKED POLYAETHYLENE FOR ELECTRICAL CABLES - Google Patents

Abstract

Process for the preparation of an insulation made of radiation-crosslinked polyethylene for electrical cables, wherein crosslinking additives for reducing the radiation dose are added. The invention is intended to make it possible to use an insulating mixture which has a good beam yield during crosslinking and good thermal aging behavior at low production costs. Taskgemaess esters of phthalic acid are added. According to the invention, low-density polyethylenes 0.5-10%, preferably 0.8-2.5% terephthalic acid dialkyl ester or dimetallyl ester or mixtures thereof with 0.1-50% Terephthalsaeurealkyl-allylester or Terephthalsaeurealkyl-metallylester be added. As an application is preferably the Elekrotechnik u. d. Other plastic processing industry into consideration.

Description

Process for the preparation of insulation from radiation- crosslinked polyethylene for electric fences _; ;

Field of application of the invention

The invention relates to a method for producing a Iso lation of cross-linked polyethylene with crosslinking reinforcing additives for electrical cables "These additives allow to reduce the required for achieving the technically required Min deotvernetzungsgrades insulation dose to reduce the proportion of the formed during the irradiation Hadiolysegase in keep technically manageable quantities.

Characteristic of the known technical solutions

To high-quality insulation from radiation crosslinked PS too. are received, radiation doses of 20 Mrad are necessary for ΡΞ low density. If, by adding suitable crosslinker activators, it is possible to reduce the radiation dose required to achieve a sufficient degree of crosslinking, this is an essential advantage with regard to the hadiolysis gases released in the crosslinking of ΡΞ. From the literature, it can be seen that the normal volume of the radiolytically split-off hydrogen at 20 Mrad of PE is about the same as the irradiated PE-volume, in particular when irradiating larger wall thicknesses possibly as a result of relatively large amounts of gas released during irradiation and the length of the dicitrogenation path, technological difficulties in Zabelvernetzung occur,

It is known Zabelisolierungen made of PE by Susatz of orga African Hadikalbildnern and a subsequent "Tärmedruckbe-

treatment or by treatment with high-energy radiation. These two methods are industrially introduced. The aim of the PS networking is to increase the continuous operating temperature of the Eat> el to 90 ° C and to set the permissible short-circuit temperature to 250 ° C. Power cables with an insulation made of non-cross-linked PE can only be used for up to 70 ° C and only for a short-circuit temperature up to max. 155 C approved.

The property values of networked! PS are internationally standardized according to the guidelines of the IEC document Hr, 2OA (Central Office) 30. The degree of crosslinking of PS is verified by HC Ir. 2OA (Central Office) 30 with the so-called thermal expansion test. Thereafter, a sample may be defined

2 dimension at a load of 20 F / cm after a 15 minute Ti treatment at 150 C have expanded at the most by 20075. To meet this requirement, a certain minimum amount of crosslinks must be generated. When crosslinking with high-energy radiation, a certain minimum dose of radiation is required. Since the available irradiation dose is limited by the efficiency of the electron accelerators when crosslinking with high-energy electrons, the production rate is thus limited in the continuous production of cables with insulation of radiation-crosslinked PS.

It is also known, to increase the crosslinking density, to add polyfunctional unsaturated monomers to the PE, in particular compounds containing a plurality of Ally I points. According to the state of the art, triallyl cyanurate, triallyl phosphate, diallylidenepentaerythritol, o-phthalate diallyl ester, 2,4-dienoxy-6-aminoalkyl-s-triazines, IT ₅ lT ^T -3is (2 ₃ 4-dienoxy-s) triazine-6) -diamine, allyl or methallyl ester-containing polymers including polyunsaturated compounds used, (S3-PS 855 793, DT-AS 1 235 177, G-Kerrutt, rubber and rubber, plastic 24, 384-387 (1971 ), DT-OS 2 308 576, DT-OS 2 308 525 and DT-AS 1 669 843).

The most commonly used additive with the best effect is triallyl cyanurate as an important factor

the use of triallyl cyanurate is the incomplete reaction of the third allyl group, which deteriorates the thermal aging behavior of the polymer, since initiated by the unreacted in the cross-linking allyl groups autoxidation, which can have a negative impact on the long-term behavior of the insulation. Another major factor of the TAG is the high price and the poor machinability and compatibility with regard to polyethylene. "Chemical modifications of the TAC are currently leading. for improving the properties, e.g. for better storage stability of the compounds; However, the effectiveness for improving the radiation yield (ratio of crosslinking sites to the radiation dose) is always reduced and the price is increased even further. Furthermore, the diallyl o-phthalate have a low crosslinking efficiency, because the diallyl o-phthalate are much more prone to cyclization reactions at the processing temperature of the polyethylene and thus lost the Yernetzungsprozeß (see, eg Simpson, W. and Holt, T ", J. Polymer Sei» Bd 18 (1955) 335; Matsumoto, A. et al., J.ehem. Soc., Japan, pure Chem. Sect., Vol. 90 (1969), p.290).

Object of the invention

The solution according to the invention should make it possible to use a radically cross-linked polyethylene insulating mixture which has a good beam yield in the cross-linking process and good thermal aging behavior and is low in the production costs

 Explanation of the invention of the invention

The invention has for its object to develop an insulation of radiation cross-linked polyethylene, in which the addition of esters of phthalic acid, the beam yield is increased. According to the invention, this object is achieved by the fact that low-density polyethylene 0.5 - 1095, preferably 0.8 - 2.555 diallylester or -dimethallyl terephthalate or their mixtures with 0.1 - 50 $ Terephthaisäurealkyl-allylester or, Terephthalsäurealkyl-methallylester (- alkyl = -methyl, -ethyl, -isopropyl) are added. The compound additionally contains aging stabilizers and / or fillers.

 "- 4 -

It proves to be particularly expedient and economical to obtain the ester mixtures obtained in the transesterification of dimethyl, diethyl or diisopropyl terephthalate with allyl or methallyl alcohol with a content of 0.1-50 % of alkyl (= methyl, ethyl, A '). methylene-, isopropyl-) allyl- or -methallyl terephthalate to be used. · Biese Mixtures are, after transesterification, purified by simple distillation, for example via a thin-layered column, and then added to the polyethylene prior to processing. By using the described isolation mixture, it is possible to use only 15 Mrad instead of the usual irradiation dose of about 20 Mrad, while maintaining the elimination of the technological difficulties encountered by radiolysis gases at 20 Mrad, the production can be speeded up increased by $ 25 in the production of networked wires from Eabelm.

The invention will be explained in more detail below using an exemplary embodiment.

Embodiment:.

1st example

From a mixture of 100 parts of low density polyethylene with an EFI of 0.25, 0.2 part of H, if-di-2-naphthyl-p-phenylenediamine and 1.0 part of an ester gum of 80 weight percent diallyl terephthalate and 20 weight percent methyl allyl terephthalate are prepared plates of 1 mm thickness and these irradiated with a dose of 15 Mrad in an electron accelerator.

The most important properties of this insulating mixture are contained in the following table. Physical Properties:

Tensile strength, kp / cm 214 Tensile strength after 10d at 150 ° G, kp / cm ² 199 Elongation at break, % 490 Elongation at break after 1Od at 150 ° G, % 456

Degree of conversion according to IEC 2OA

(Central Office) 30 (Hotset

read with 20IT), # 110

- 5 -,

Yerlust factor tan S

2O ⁰ C 5,8.ΙΟ "" ⁴

5O ⁰ C 4.5.10 ~ ⁴ .

7O ⁰ C 3,8.10 ~ ⁴

9O ⁰ C '5.2.10 " ⁴

2nd example

From a mixture of 100 parts of low-density polyethylene with the MFI 0.25, 50 parts of filler, 0.3 parts of polymeric 2,2,4-trimethyl-1,2-dihydroquinoline and 1 part of an ester mixture of 80 wt. % diallyl terephthalate and 20 wt.% methyl-allylterephthalat be plates of 1 mm thickness is produced and this is irradiated with a dose of 14 Mrad in an electron accelerator.

The most important properties of this insulating mixture are contained in the following table.

Physical properties :

ο Tensile strength, kp / cm 146

Tensile strength after 7d

at 135 ^° C., kp / cm ² 155

Elongation at break, % 400

Breaking strain after 7d

- at 135 ⁰ C, % 365

Degree of crosslinking according to IEC 2OA (Central Office) 30 (Hot set test with 4Oi ¹ O, % 135

3rd example :

An Al conductor of section 185 mm is coated with a conductive copolymer layer and isolated with a polyethylene mixture according to Example 1. The wall thickness of the insulation without smoothing is 3.8 mm. The crosslinking of the insulation takes place with an electron accelerator. The electron energy is 2.3 HeV, the beam current 16 mA. At a withdrawal speed of 8 m / min, the surface dose is 15 Mrad. Continuous production of all standardized production lengths is possible.

Claims (2)

Invention claim: 1. A process for the preparation of a radiation of cross-linked polyethylene for electric zabel, characterized , characterized in that low-density polyethylene 0,5 - 10%, preferably 0.8 -2.5 he fo terephthalic diallyle st respectively, -dimethallylester · or mixtures thereof with from 0.1 to 50 - # Terephthaisäurealkyl allyl ester or Terephthalsäurealkylmethallylester (- alkyl = -methyl, -ethyl, -isopropyl) may be added » 2. The method according to item 1, characterized in that the compound additionally contains aging stabilizers and / or fillers. .