DE1704478A1 - Process for the production of profiles from foam - Google Patents

Description

Process for the production of profiles from foam It is known to produce foamed profiles or line insulation from low density polyethylene, by surface-coating granulated polyethylene with an adhesion promoter (e.g. Paraffin, rutyl stearate or low-viscosity polyisobutylene oil) and then impregnated a chemical propellant powder. Chemical blowing agents include such substances to understand that form gaseous products when heated, e.g. azo, nitroso, Azido or hydrazo compounds. Then the so treated is granulated Polyethylene is homogenized in the extruder and the plasticized mass is molded Squeezed and foamed in a room of low pressure. Disadvantage of this The method is that during the transport from the mixing plant to the extruder or the impregnated polyethylene granulate blowing agent in the feed hopper of the extruder is lost and partially segregated, causing unevenly foamed profiles develop.

It is also known to first mix the propellant with the plasticized one To homogenize plastic, e.g. in a kneader, extruder or on a mixing mill. You then get vibration-proof Mixtures, so-called "compounds", which then also with an extruder in the manner described above to form foams can be processed. However, it is not possible to homogenize this twice To obtain foam body with a finer cell structure than after the aforementioned Method of powdering the chemical blowing agents using an adhesion promoter.

Finally, there is a method for producing foamable molding compositions known from powdered polyolerines which have a grain size of up to 85 percent by weight below 150 / u, by incorporating a powdery propellant as well Optionally customary additives in an optionally heated mixer, which thereby is characterized in that one in the powdered polyolefins, the blowing agent as well if necessary, incorporates the additives until sintering. The propellants must be used are heated very high, which is perceived as a particular disadvantage. Also is a complete homogenization in the melt and the subsequent production of coarse granulate not possible.

It has now been found that foam profiles can be produced by heating propellant-containing olefin polymers and cooling with shaping advantageous can be prepared by powdery mixtures prepared at room temperature extruded from blowing agents and olefin polymers.

The foam profiles produced according to the invention have a homogeneous closed cell structure. Compared to the previously usual procedures the many advantages described here.

1. There is no longer a need for a bonding agent, so it's just for preparation there is no working cycle for the propellant intake.

2. The incorporation of the propellant into the powder can be done in simple, even makeshift devices such as roll barrels, shaker flasks, or others primitive mixers.

3. You can work at normal temperature. This is how it is possible to also use propellant systems in the processes described above the melt or sinter homogenization due to premature decomposition or react in an uncontrollable manner, so that the resulting "compounds" have very different propulsive abilities.

4. The cell structure is very even and significantly finer than that of the procedures that correspond to the state of the art.

5. Surprisingly, the advantages mentioned under 4. also remain then obtained if you still have a melt preparation for the production of coarse-grained Cylindrical granulate or cubes (approx. 3 x 3 mm or 4 mm edge length) are then connected.

This new processing method could be based on previous experience cannot be foreseen, because it was considered certain that during the homogenization (when dispersing) two components the best mixing effect is achieved when at least one component is in the liquid phase.

The method according to the invention is also suitable for training others Usual additives, e.g. of dyes, antistatic agents, fibers, stabilizers against light and / or heat aging, crosslinking agents or fillers in powdered form Polyethylene.

Suitable olefin polymers include homo- and copolymers of e.g. ethylene, xethylene vinyl acetate or ethylene t-butyl acrylate.

Chemical blowing agents are to be understood as meaning those in the Heat form gaseous products, e.g. azo, nitroso, azido or hydrazo compounds, also hydrated salts or ionic compounds, which are obtained by salting or thermal decomposition release volatile components, e.g. ammonium bicarbonate, sodium bicarbonate, Sodium sulfate. 10 H20, calcium carbonate, magnesium carbonate or mixtures of sodium carbonate or bicarbonate with organic or inorganic acids.

For mixing powdered olefin polymers and chemical blowing agents Conventional mixing devices can be used, e.g. Tumble mixers, roller barrels, Stirrers, shaker flasks or high-speed refrigerated mixers.

The profiles are e.g. Moldings understood molded articles produced, e.g.

Rods, rods, tubes, plates or foils.

Customary processes are used to produce the profiles from foams and devices used. Screw extruders are preferably used as extrusions used in which the powdery Mixture of olefin polymers and blowing agent plasticized and under pressure by a conventional molding machine is pressed into a room of low pressure and foamed there. It is also possible, when using propellants with a relatively high decomposition product, the powder to be processed on calenders and in a connected operation through the action of heat to foam in a known manner.

The foam profiles produced according to the invention are suitable for example for the insulation of electrical conductors, for the production of Seals, decorative films or tapes, etc.

The parts mentioned in the examples are parts by weight.

Example of the experiment is carried out with a polyethylene powder, which has a melt index of 1.5 and a density of 0.918. It has the following Grain size distribution: 5 ffi 750 / around 10% 750 - 500 / around 17 4% 500 - 300 / around 18% 300 - 200 / by 30% 200 - 100 / by 12% 100 - 60 / by 7 ffi 60-40 to 99% to 100 parts of the powder described, which has sufficient flowability, 1 part of a propellant based on a diphenylene disulfohydrazide (e.g. Diphenyl ether -4,4'-disulfonic acid hydrazide) was added and shook briefly to make it uniform dispersed in the plastic powder. The powder is on an extruder of 30 mm diameter at 30 rpm. and the following temperature program processed: 110, 140, 180, 170, 1700C nozzle: round nozzle 1.9 mm diameter.

The foam profile has a diameter of 4 mm. The cell structure is uniform, the cell diameter is 30 to 40 / µm, the density of the profile is 0.41 g / cm3.

Comparative example on 100 parts of polyethylene wilrfelgranulate with an edge length of 3 to 4 mm, a melt index of 1.5 and a density of 0.918 are in a Rollraß with 0.5 parts of a low viscosity polyisobutylene oil or also moistened with butyl stearate. Duration approx. 5 to 10 minutes. Now becomes a part the same chemical blowing agent as in Example 1 was added and repeated Roll evenly on the granules that have become sticky due to the adhesion promoter distributed.

Duration approx. 15 to 20 minutes. The floating granules are placed on the processed into a foam profile in the same machine under the same conditions. The profile obtained has a coarser cell structure than the profile after the first one Procedure. The cell diameter is 50 to 90 µm. the density of the profile is 0.47 g / cm3.

Claims (1)

Method for producing profiles from foams by heating olefin polymers containing blowing agents and cooling while shaping, characterized in that pulverulent mixtures prepared at room temperature extruded from blowing agents and olefin polymers.