NO781871L - MATERIAL FOR PREPARATION OF FOAMED INSULATION - Google Patents

Abstract

Mixture for making foam insulation

Description

The invention relates to a polymer-based mixture for the production of foamed cross-linked insulation for metal pipes and electrical conductors.

For insulation purposes, electrical conductors and metal pipes are provided with a plastic layer. In order to increase the insulation value and save the polymer material, foamed materials or foam plastics have been used more and more in the past as insulation materials;

but neither temperature resistance nor mechanical resistance nor degree of foaming have so far been satisfactory.

For these reasons, it has already been proposed to cross-link the polymer materials.

The object of the invention is to provide a mixture

which can be processed in an extruder and can be foamed to a high degree of foaming and a relatively low volume weight, thereby providing both material savings and high temperature resistance.

The solution to this task is a mixture that consists

of 0 - 80 parts hard polyethylene, 100 - 20 parts soft polyethylene,

1 to 5 parts propellant and 0.1 - 2 parts crosslinking agent.

A polyethylene that is marketed under the name "Lupolen 5011 K" is advantageously used as hard polyethylene. As soft polyethylene, a polyethylene is used with advantage which is marketed under the trade name "Lupolen 2425 MX". The chosen ratio between hard polyethylene and soft polyethylene is based on the requirements placed on the insulation material. While a mixture with a higher proportion of hard polyethylene is harder and is characterized by higher temperature resistance, the advantage of using relatively more soft polyethylene consists of better flexibility. Especially when the pipes or cables are to be used for furnishing homes, it has proven beneficial to add the mixture 4-15 parts fire retardant. By adding the fire-preventing or flame-reducing agent, the flammability of the insulation jacket is significantly reduced. As a propellant

dicarbonamide has thus proved particularly beneficial. Cross-linking. the agent is advantageously a 1,3-bister. butylperoxyisopropylbenzene. The combination of this propellant and said cross-linking agent

■ ensures that the polymer mixture when heated first at least

partially cross-linked and only then foamed. Due to this ratio, the relatively low volumetric weight is achieved on e.g.

200 kg/m . As a flame retardant, a mixture of 3 - 10 parts decabromodiphenyl ether and 1 - 5 parts antimony trioxide has been found to be particularly effective. A mixture that has proven to be optimal both with regard to bending capacity and temperature resistance as well as chemical resistance consists of 50 - 70 parts hard polyethylene, 30 - 50 parts soft polyethylene, 2-4 parts azodicarbonamide, 0.3 -

0.7 parts of 1,3-bis-tert.-butylperoxyisopropylbenzene, 4-7 parts of decabromodiphenyl ether and 3-4.5 parts of antimony trioxide.

The invention shall be described in more detail by means of an example.

A mixture of 60 parts hard polyethylene (Lupolen 5011 K), 40 parts soft polyethylene (Lupolen 2425 MX), 3 parts azodicarbonamide, 0.5 parts 1,3-bis-tert.butylperoxydiisopropylbenzene, 5.7 parts decabromodiphenyl ether and 3.8 parts antimony trioxide which may have small amounts of anti-aging agent added, is carefully mixed in a mixer and heated to a temperature of 130° C. From the mixer, the plastic mixture enters the extruder head which contains a rotatably supported mandrel.■ The mandrel or core has a continuous axial bore through which the metal tube or the copper wire to be insulated is passed through. During the transport in the extruder head from the filling opening to the nozzle, the polymer mixture is heated due to the prevailing shear forces of the mixture. The temperature of the polymer mixture at the exit from the nozzle should be 190 - 200° C. Already at 190° C, the decomposition of the cross-linking agent begins, which causes the melt to begin to cross-link chemically. At approx. At 180° C, the azodicarbonamide decomposes and gives a gas that appears foamy. Due to the fact that the cross-linking of the polymer mixture has already begun, the viscosity of the melt has increased so that a larger part of the released gases from the azodicarbonamide remain in the polymer mixture and the degree of foaming can thereby be increased significantly. At the exit from the extruder, the degree of cross-linking should

be 10% so that the mixture from the nozzle does not drip from the pipe or copper wire. With the initial chemical cross-linking of the mixture, a polymer layer with uniform wall thickness can be obtained over the whole. After exiting the extruder, the mixture is further cross-linked and a cross-linking degree of 50% can be achieved.

The mixture is particularly suitable for the production of insulating layer 1 for house installation pipes 2 made of copper (see fig. 1). The mixture can also be used as a starting material for insulation jackets 3 around low-current lines 4' (see fig. 2).

The mixture is particularly distinguished by the fact that an exceptionally high degree of foaming can be achieved, i.e. low volume weight, of 200

kg/m and below. The mechanical strength is only slightly less than that of pure polyethylene. A significant advantage that is particularly important for installation pipes is the high temperature resistance. Insulating layers produced according to the invention are temperature-resistant up to 130°C.

Claims (7)

1. Foam insulation mixture consisting of 0 - 80 parts hard polyethylene, 100 - 20 parts soft polyethylene, 0.5 - 5 parts propellant and 0.1 - 2 parts cross-linking agent, for the production of foamed, cross-linked insulation for metal pipes and electrical conductors. 2. Mixture as stated in claim 1 consisting of 50 - 70 parts hard polyethylene, 30 - 50 parts soft polyethylene, 2-4 parts propellant and 0.3 - 1 part crosslinking agent. 3. Mixture as stated in claim 1 or 2, characterized in that 4 - 15 parts of fire retardant have been added. 4. Mixture as stated in the preceding claims, characterized in that azodicarbonamide is the propellant. 5. Mixture as stated in claim 1 or the following claim, characterized in that the cross-linking agent is 1,3-bis-tert-butylperoxyisopropylbenzene. 6. Mixture as specified in claim 1 or the following claim, characterized in that a mixture of 3 - 10 parts of decabromodiphenyl ether and 1 - 5 parts of antimony trioxide (Sb2C>2) is used as a fire extinguishing agent. 7. Mixture as specified in claim 1 or the following claim consisting of 50 - 70 parts hard polyethylene, 30 - 50 parts soft polyethylene, 2-4 parts azodicarbonamide, 0.3 - 0.7% 1,3-bister. -butylperoxyisopropylbenzene, 4-7 parts decabromodiphenyl ether and 3 - 4.5 parts antimony trioxyd.