CS205707B1 - Thermo-oxidation stabilized ramificated polyethylene alleviated by the disintegration products of thr thermoact - Google Patents

Description

The subject of the invention is chemically lightened branched polyethylene stabilized against thermo-oxidative destruction. The purpose of the invention is a solution where the possibilities of adverse reactions of the starting materials and the interaction of radical splines of the decomposition of the thermoreactive component with the antioxidant, manifested by the negative influence of the supernatants on the thermooxidative aging of the polymer, are eliminated. The solution is to enable the production and application of suitable glazed materials of this type, especially in the field of manufacture and use of branched and expanded polyethylene insulated wires and cables, where in addition to electrical properties thermo-oxidative stability at elevated temperatures plays an important role.

Polyethylene is a material with very good electrical and mechanical properties, is easy to process and has a relatively low cost, its application in electrotechnik®, especially in buckling is very wide. Branched polyethylene has a low dielectric collision factor with a very low frequency dependence, and therefore to a significant extent satisfies the function of a suitable dielectric in high-frequency conductors and cables. To improve the transfer properties of such products, a material having a reduced dielectric permittivity is often required. This property can be achieved, for example, by filling such a material with air, i.e. by lightening it, in optimum cases up to approximately one-half of the initial bulk density of the polymer. The lightweight insulation which is applied to the core by extrusion technology, in the case of polyethylene, is best obtained by applying the mixture

205 707

205 707 β containing thermoreactive substances which produce gases blowing through the melt by thermal decomposition.

However, for polyethylenes chemically fed and containing antioxidants, however, there are severe difficulties due to the thermoreactive nature of the blowing agents. In particular, mixtures of amine antioxidants may not be used at all here, since in their presence an oxidoreduction strand of the blowing agent occurs in a form which, by thermal decomposition, no longer produces gaseous fumes in the material. Although the content of phenolic antioxodants in the mixture does not lead to complete deactivation of the blowing agent, serious drawbacks occur here as a result of the reaction of the radical products of the decomposition of the blowing agent with the antioxodant to substantially paralyze their stabilizing activity in the material. In order to achieve the desired durability of such a lightweight polymer under thermal stress, the proportion of antioxidant in the mixture should be overdosed so that the material contains up to several times the usual amount. However, the use of such mixtures with high concentrations of phenolic antioxidants, whose solubility in the polymer is greatly limited, is very disadvantageous. This is because the antioxidant migrates from the polymer, thereby gradually losing its thermo-oxidative stability, and with such a material the desired and required properties are no longer achieved. ...

The disadvantages of the prior art according to the invention are eliminated by a solution in which the modified polyethylene component is dispersed in the polymer melt in a proportion of 0.3 to 3% by weight of a blowing agent, which is p, p * -oxybis (benzenesulfonylhydrazide).

together with a proportion of 0.05 to 0.5% by weight of a phenolic antioxidant and a hydroxyl group protected in the o-position by tertiary butyl, for example 2,2'-thiodiethyl-bis-C3- / 3,5-di- tert-butyl-4-hydroxyphenyl (propionate, 4,4-thio-bis-6- (tert-butyl-m-cresol)), or tetrakia- (methylene-3-) 3,5-di-tert-butyl-4-hydroxyphenyl -propionate // methane.

The mixture with the proposed components and fractions does not interact with either the starting materials or their decomposition products and therefore the antioxidant is not exhausted from the mixture when the blowing agent breaks down. In addition, the decomposition products of the blowing agent form, with the antioxidant, an aynergic mixture, the action of which exhibits a very advantageous, i.e. two- to four-fold, increase in the effectiveness of the antioxidant. This synergistic effect is even two-sided, because in the same US it is also manifested in terms of increasing the blowing agent efficiency, ie by 20 to 30%. The physical properties and the processability of the polymer do not adversely affect or affect the use of conventional and other additives, if these are of an inert nature.

Further details and conditions relating to the preparation and obtaining of the tarmooxidation-stabilized, chemically-lightened branched polyethylene are given in the following examples, in which the substance and the nature of the solution according to the invention are specified. Branched polyethylene in accordance with 8 of ČSN 64 3010, paragraph 1, means a defined type of low-density homopolymer produced by high-pressure polymerization.

Example 1

Polyethylene demonstrating the solution and stabilization results achieved by thermo-oxidative destruction in chemically lightened material has the following characteristics: flow index 2.1 g / 10 minutes, density 0.921 g / cm ^3, and induction period of oxygen absorption at 200 ° C below 0.1 hours. For the preparation of the test samples e and proceeding, after melting the polyethylene at 130 ° C, 1% by weight of p, p * -oxy-bis- (benzenulfonylhydrazide) and 0.1% by weight of 2,2 * thiodiethylbis were added in a Brabender plastograph kneading chamber. - [3- (3,5-di-tert-butyl-4-hydroxyphenyl) -propionate. mieáaní polymer and ⁵ · r 'with the ingredients continued for five minutes. The mixture thus obtained was used directly to determine the induction period of oxygen uptake, which at 200 ° C had a value of 1.4 h and after a 5 minute breakdown of the blowing agent at 160 ° C for 5 to 2 h. however, in the absence of the blowing agent, the time was only 0.9 h. The degree of lightening of the polyethylene of the composition described was determined by the density of 1.9 mm thick insulation applied by extrusion of a copper conductor of 1.1 mm diameter using an extruder with 63 mm diameter. L / D 20 at 120, 140 and 160 ° C zone temperatures and 140 to 150 ° C heads and nozzles. The material drawn under the above conditions had a bulk density of 0.552 g / cm ³ and in the absence of an antioxidant 0.607 g / cm ³ .

Example 2

The same type of polyethylene was applied and the same test sample preparation and evaluation procedure was used as in Example 1. 1% by weight of p, p * -oxybis-benzenesulfohydrazide was added to the polyethylene, but 0.2% was used to stabilize the polymer. The induction periods of oxygen uptake at 200 ° C were as follows: 2.7 h before pulling the polymer 9.9 h after disintegration blowing agents and 1.9 h in the absence of the blowing agent. The bulk density of the extruded copper conductor insulation of the above dimensions was 0.501 g / cm ³ .

Example 3

Following the same procedure as in the preceding examples, the same types and amounts of antioxidant were used but the polyethylene was readily blend containing 1.3% by weight of p, p-oxybia-benzenesulfohydrazide. The induction periods of oxygen uptake at 200 ° C that aa in this case measured were as follows:

2.9 h before the blowing agent disintegrates, 11.5 h after disintegration and 1.9 h in the absence of the blowing agent. The material drawn by such a blowing agent content had a bulk density of 0.442 g / cm ³ .

Example 4

In the same manner as in all of the foregoing examples, the thermooxidation stability of 1'washed polyethylene was verified using 1.5% by weight of β, β-oxy-bis-benzenesulfohydrazide as blowing agent and 0.25% by weight of 4,4'-thio-bis]. 6 tert-butyl-m-cresol as an antioxidant. The induction period for oxygen uptake at 200 ° C was 6.6 h for polyethylene tightening, after blowing up of the blowing agent 17.8 h without blowing agent, but in the presence of antiZOS 707 oxidant 4.2 h. The bulk insulation weight was 0.38 g. / em ^ and without using antioxidants 0,44 g / cm \

Example 5

The difference from the previous examples was in the composition of the 1% wettable mixture containing 0.8% by weight of β, β-oxy-bis-benzenesulfohydrazide and 0.15% by weight of tetrakia-β-methylene-3- / 3,5-di-tert-butyl ester. Butyl 4-hydroxyphenylpropionate / methane The thermo-oxidative stability of the mixture, characterized by an induction period of uptake of the alkali at 200 ° C for the lightened polymer, was 2.5 h, after blowing the blowing agent 8.8 h with no blowing agent 2.1 h. reached a bulk density of 0.64 g / cm 2, respectively. 0.70 g / cnP in the absence of antioxidant.

The treatment of the components of the polymer with the solution according to the invention will, and in any case, have a very positive effect on the achievement of advantageous electrical and mechanical properties and suitably eliminates the existing drawbacks. The application of this solution does not require either special production facilities or is connected with the withdrawal of the technological process during production and processing, respectively. application of the polymer, thereby giving suitable conditions for immediate use in the field of cable industry and, at the same time, directly to the producers and suppliers of these materials.

Claims (1)

Object of the invention Thermo-oxidized stabilized branched polyethylene, lightened by the decomposition products of the thermoreactive blowing agent, suitable for high-frequency electrical and cable purposes, characterized in that the mixed component of polyethylene is a dispersed proportion of 0.3 to 3% by weight of the blowing agent; oxy-bia- (benzenesulfonylhydrazide) ₂ NH - NH - SO; O o · ° -O> oleic antioxidant i SO ₂ - NH 1 ₂ , together with a proportion of 0.05 to 0.5% by weight of the phenolic antioxidants and the hydroxyl group of the atheroid protected in the tertiary butyl (e.g., 2,2% - thiodiethyl-bia-) 3 (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], 4,4'-thio-bia-6- (tert-butyl-m-cresol), or tetrakis (methylene-3-) 5-di-tert-butyl-4-hydroxyphenyl propionate / methane. Price: 2,40 Kčs Printed by Moravian Printing Works, plant 12, Leninova 21, Olomouc