DE1629367A1 - Process for the continuous production of crosslinked polyolefin foams - Google Patents

Description

Troisdorf, the Ί

Τ6 ~ 293 ¥ 7

• DYNAMIT NOBEL AKTIENGESELLSCHAFT
Troisdorf / Bez «Cologne

Process for the continuous production of crosslinked Polyolefin foam

It is "known to use polyethylene foams in a continuous process with the help of ionizing rays to network «The Irradiation can either be before or after foaming be made. However, this method has the disadvantage that only "with relatively thin masses a uniform Networking is achieved »

According to another process (French Patent 1,409,982). It is' well known that one can extrude a cross-linked with a peroxide polyolefin composition to a crosslinked foam body when the procedure is as follows: The polyolefin is swollen with an organic solvent [medium and then Blowing agents and crosslinkers are incorporated into the compound · The swelling of the compound with an organic solvent proves to be necessary because it involves the incorporation of the crosslinker

I ■ j

maintenance of its light-off temperature, whereby ^!

premature crosslinking of the composition is avoided · encryption \ applies πφη low boiling organic substances as propellants i, then the required. Familiarization with this already _; German. eep. Extruder preplasticized material through a "',

in the decompression part of the Schneoken-

008088/1748. "~ ^{AL 1NSPECTED} ■]

The invention now relates to a process for the continuous production of foams from crosslinked polyolefins and / or olefin copolymers, blowing agents and peroxide crosslinkers and optionally fillers, pigments, anti-aging agents and sulfur using an extruder, which is characterized in that the peroxide in a below 40 ⁰ C boiling propellant dissolved and pressed through a filler neck in the Dekampression part of the screw cylinder to the already melted and homogenized polyolefin material in the feed and compression part of the screw and incorporated by the screw into the mass and that in the gel-like mass thus obtained The decomposition of the peroxide and thus the crosslinking of the mass is controlled by temperature control so that the mass just remains flowable and a dimensionally stable foam strand is obtained when it is ejected. The foam is then kept at an elevated temperature for so long s set until networking is complete ₉

Surprisingly, it has been found that the process According to the invention, a crosslinked polyolefin foam is obtained without the polyolefin composition beforehand still has to swell with an organic solvent «

The melting process can therefore be carried out without regard to the crosslinking agent. The gel formed after the addition of the propellant / oxide solution has such a low viscosity that there is no uncontrolled prolonged exposure during the mixing and incorporation! . he follows. The temperature can be controlled externally via the cylinder heating and controlled so precisely that with 009886 / _ma ORWINAL, NSPECTH)

Knowledge of the decay curve of the peroxide and the residence time of the mass in the tendon cylinder, a certain degree of crosslinking is achieved _o The crosslinking should proceed so far that on the one hand the gel-like mass still retains sufficient flowability for perfect shaping in the injection mold and on the other hand the resulting foam body as a result of the is dimensionally stable due to the partial crosslinking achieved material strength and no longer collapses. In this way, it is possible to expose the foam product to an elevated temperature until the crosslinking is complete, without its shape undergoing any further change.

Polyolefins such as low-pressure and high-pressure polyethylene, polypropylene, mixtures of polyolefins and olefin copolymers are suitable as starting materials. ι liquids such as tricilormonofluoromethane, diclorodifluoromethane, dichlorotetrafluoroethane or mixtures of two or more of these substances are used «

ORIGINAL BATHROOM - 4 -

009886/1748

The following organic peroxides are suitable crosslinkers:

Dialkylperoxyde having tertiary carbon atoms, for example, ₀ dicumyl peroxide, di-t-butyl peroxide, di-t-amyl peroxide, 2,5-dimethyl-2,5-di-t-butylperoxy-hexane, cumyl-t-butyl peroxide and other »

For the crosslinking of polypropylene or polypropylene copolymers sulfur is necessary as a synergent to the peroxides. The sulfur is expediently together with the Polyolefins, fillers, pigments and anti-aging agents put in the extruder »

Fillers and pigments influence the properties of the Foam body and have, for the incorporation and distribution of the propellant as well as for the formation of the cells Meanings Examples of possible fillers are:

Carbon black, metal oxides, metal carbonates, metal silicates and Metal phosphatesβ

Those compounds from the series of polyolefin stabilizers are used as aging inhibitors, which no or only an insignificant reaction with the peroxy radicals of the crosslinking agent. »Suitable substances include: the following: polymeric 2,2,4-trimethyldihydroquinoline, 6 ~ phenyl-2,2,4-trimethyldihydroquinoline, 4,4-thio-bis- (6-t-butyl-3-methyl-phenol), 2,2-thio-bis - «(4-methyl-6- t-butyl-phenol), Phenyl-Ck- and ß- «naphthyl-amine, Di-ß-napthyl-p-phenylene-diamine, diphenyl- and phenyl-cyclohexyl-p-phenylene-diamine, 2-mercaptobenzimidazole

ORIGINAL! NSFECTED 009886 / 17Λ8

example 1

100 j-EWO parts back pressure polyethylene are mixed with 5 wt _o parts by carbon black in a fluid mixer The mixture is in a Heiige of 6 kg / h into the hopper of a screw press dosed with a screw having a diameter D = 36 mm and a length of 25 x D is equipped «The worm has a retraction cone, compression, decompression, 2“ compression and au strare ζ one on “The tendon cylinder is in the area of the M: oi7iproü £ ioiiszone with an inlet port for the propellant vex ^ seherio

The entered mass is melted by the screw in the Einzugurid compression part, the mass ^{temperature rising to about 170 0} C ^ A 15 ⁰ G warm solution of 100 parts by weight of trichloromonofluoromethane and 3 »6 parts by weight of dicumyl peroxide is then poured through the propellant nozzle amount of 1.5 kg / h was added with a metering pump so that a mixing ratio of 100 weight parts _o ~ polyethylene Gewo to 25 parts blowing agent and 100 wt "- polyethylene parts to 0.9 parts by weight of crosslinking is achieved . In the compression and discharge part of the screw, these components are intimately mixed, whereby the pressure in the direction of the injection tool increases ο A gel is created, the temperature of which is kept constant at 165 ° C. The free radicals of the decaying peroxide initiate the cross-linking of the polyethylene, proceeds up to the inlet into the 12O ⁰ C hot injection molding tool. Here, the mass is networked to such an extent that it has just sufficient flowability for perfect shaping

009 886/174 8 bath original

of the tool, the blowing agent, which evaporates as a result of the pressure relief, inflates the strand in a foam-like manner »Die Cell walls have such a high strength that the crosslinking can be completed by subsequent further heat treatment without affecting the cell structure or still change the shape of the foam strand. The resulting foam has very small, even, closed cells and a density of 0.045 g / cm "

Example 2

100 GeWo parts of low pressure polyethylene is mixed with 1 part by weight of zinc stearate and 0.5 wt ¹ ^ rush 4,4-thio-bis- (6-t-butyl-3-methylphenol), and in an amount of 6 kg / h metered into an extruder analogous to Example 1 _o As

Blowing agent and crosslinking agent is a solution of 50 parts by weight _o trichloromonofluoromethane, 50 parts by weight dichlorodifluoromethane and 6 parts by weight of 2,5 ~ dimethyl-2,5-di- (t-butylperoxy) hexane in an amount of 1 , 2 kg / h "added the temperature of the mass is maintained by the filler neck of the blowing agent to the injection molding tool to 162 ⁰ C? the tool itself has a temperature of 115 ^° C. The exiting crosslinked foam has small, uniform, closed cells and a density of 0.05 g / cm. It is subjected , as indicated in Example 1, to a subsequent heat treatment for final crosslinking.

Example 3

100 parts by weight of a misoh polymer from 87 parts by weight of ethylene and 13 parts by weight of vinyl acetate are mixed with 45 parts by weight of a neutral aluminum particle, 5 parts by weight of titanium dioxide, 1.5 parts by weight of oaloium sttarate and 0, 8 wt.

009886Z ₇ IJAA

Parts of polymeric 2,2,4-trimethyldihydroquinoline in mixed in a kneader and then granulated. In an extruder analogous to Example 1, 6 kg per hour this granulate and 2 kg of a solution of 100 parts by weight of dichlorodifluoromethane and 6 parts by weight of di-t-butyl peroxide as a friction agent or «. Yernetzer metered o The The temperature of the mass is taken from the filler neck of the friction agent kept at 155 ° C «, The extruded foam has very small, (uniform), closed cells and a Volume weight of 0.1 g / cm. The completion of the crosslinking is analogous to Example 1 by subsequent heat storage scored

Example 4

100 parts by weight of polypropylene are mixed with 0.15 parts by weight of sulfur and introduced into an extruder analogously to Example 1 in an amount of 6 kg / h. A solution of 100 parts by weight of trichloromonofluoromethane and 4 »8 wt . parts of dicumyl peroxide in an amount of 1.25 kg dosed / h the temperature of the mass is maintained up to the injection molding tool to 158 ⁰ C. The exiting, cross-linked foam has closed cells and a density of 0.06 g / cm *

009886/1748

Claims (2)

Patentans ρ r ü. c h e: ο method -for the continuous production of foamed materials of cross-linked polyolefins and / or olefin copolymers, blowing agents and peroxidic "crosslinking agents and optionally fillers, pigments, anti-aging agents and sulfur with the aid of an extruder, characterized in that the peroxide dissolved in a below 40 ⁰ C boiling blowing agent and via a filler neck into the decompression part of the screw cylinder to the already melted and homogenized polyolefin mass in the feed and compression part of the screw and worked into the mass by the screw and that in the gel-like mass thus obtained de.r decomposition of the peroxide and thus the crosslinking the Hasse is controlled by temperature control so that the mass just remains flowable and a dimensionally stable foam strand is obtained when it is ejected ο 2. The method according to claim 1, characterized in that the foam obtained is exposed to an elevated temperature until the crosslinking is complete « Dr.Bu / Jo " 009886/1748