DE1062925B

DE1062925B - Process for reducing the stress corrosion cracking of polyethylene or copolymers of ethylene with other olefins which had been produced by low-pressure processes

Info

Publication number: DE1062925B
Application number: DEF22331A
Authority: DE
Inventors: Dr Ernst Staerk; Dr Claus Heuck
Original assignee: Hoechst AG
Current assignee: Hoechst AG
Priority date: 1957-02-12
Filing date: 1957-02-12
Publication date: 1959-08-06

Description

Verfahren zur Verminderung der Spannungsrißkorrosion von Polyäthylen oder Mischpolymeren des Äthylens mit anderen Olefinen, welche nach Niederdruckverfahren hergestellt worden waren Es ist bekannt, daß Hochdruckpolyäthylen eine starke Neigung zu Spannungsrißkorrosionserscheinungen zeigt. Process for reducing the stress corrosion cracking of polyethylene or copolymers of ethylene with other olefins, which are produced by low-pressure processes It is known that high pressure polyethylene has a strong propensity shows signs of stress corrosion cracking.

Diese äußern sich in der Form, daß auf unter Zug- oder Biegebeanspruchung stehenden Polyäthylenteilen bei Berührung mit Netzmitteln und organischen Lösungsmitteln, namentlich bei mäßig erhöhten Temperaturen (40 bis 60°C), oberflächlich Risse auftreten, welche schließlich zur Zerstörung der Kunststoffteile führen.These express themselves in the form that on under tensile or bending stress standing polyethylene parts in contact with wetting agents and organic solvents, in particular at moderately elevated temperatures (40 to 60 ° C), cracks appear on the surface, which ultimately lead to the destruction of the plastic parts.

Man hat auch gefunden, daß diese den Einsatz des Materials stark einschränkenden Störungen durch Erhöhung des Molekulargewichts und durch Zusätze von Polyisobutylen und Paraffinen weitgehend herabgesetzt werden können.It has also been found that these severely limit the use of the material Interferences due to an increase in the molecular weight and due to the addition of polyisobutylene and paraffins can be largely reduced.

Es ist weiterhin bekannt daß Polyäthylen, welches nach Niederdruckverfahren hergestellt worden ist, Spannungsrißkorrosionserscheinungen grundsätzlich in einem geringeren Ausmaße zeigt als Hochdruckpolyäthylen, was nur zum Teil auf die höheren Molekulargewichte der in der Technik gebräuchlichen Niederdruckpolyäthylene zurückzuführen sein dürfte. Einen wesentlichen Einfluß besitzt der andersartige Aufbau des Makromoleküls gegenüber demjenigen von Hochdruckpolyäthylen, welcher auch die Ursache für die erheblichen Unterschiede in den anderen Eigenschaften, wie z. B. It is also known that polyethylene, which by low pressure process has been produced, stress corrosion cracking phenomena basically in one shows smaller dimensions than high-pressure polyethylene, which is only partly due to the higher ones Molecular weights of the low-pressure polyethylene commonly used in technology should be. The different structure of the macromolecule has a major influence compared to that of high-pressure polyethylene, which is also the cause of the significant differences in the other properties, such as B.

Kristallinität, Dichte, Reißfestigkeit, Dehnung und Härte ist.Is crystallinity, density, tear strength, elongation and hardness.

Bei eigenen Versuchen wurde schließlich festgestellt, daß Niederdruckpolyäthylene, welche z. B. nach den Niederdruckpolymerisationsverfahren, die bei Raff All i -son: Polyethylene, 1956, auf den S. 72 bis 81 beschrieben sind, hergestellt worden waren, in Salzwasser bei 900 C eine starke Spannungsrißkorrosion zeigen, selbst wenn sie in Netzmitteln bei 500 C eine hohe Widerstandsfähigkeit besitzen. In our own experiments it was finally found that low-pressure polyethylene, which z. B. according to the low-pressure polymerisation process, which at Raff All i -son: Polyethylene, 1956, described on pp. 72 to 81, show severe stress corrosion cracking in salt water at 900 C, even if they have a high resistance in wetting agents at 500 C.

Aus einer Veröffentlichung in »Chemical Trade Journal Bd. 135 (1954), S. 1694 bis 1695, ist es bekannt, daß man die Spannungsrißkorrosion von Hochdruckpolyäthylen durch Zugabe von etwa 501, Butylkautschuk vermindern kann, so daß solche Mischungen für Kabelhüllen verwendet werden können. Dieses Verfahren läßt sich aber nicht auf Niederdruckpolyäthylen übertragen, da bei diesem die Neigung zu Spannungsrißkorrosion durch Zusatz von Butylkautschuk allein nicht wesentlich verringert wird. From a publication in "Chemical Trade Journal Vol. 135 (1954), S. 1694 to 1695, it is known that the stress corrosion cracking of high pressure polyethylene by adding about 501, butyl rubber can decrease, so that such mixtures can be used for cable sheaths. However, this procedure does not work Transfer low-pressure polyethylene, as this has a tendency to stress corrosion cracking is not significantly reduced by adding butyl rubber alone.

Es wurde nun gefunden, daß man die Anfälligkeit von Niederdruckpolyäthylen gegen die Spannungsrißkorrosion in Salzwasser bei 900 G in sehr starkem Umfange dadurch herabsetzen kann, daß man Zusätze von Hochdruckpolyäthylen mit einem Molekulargewicht über 40000 in Mengen von 1 bis 20O/o, vorzugsweise von 3 bis 901o, und Butylkautschuk mit einem Molgewicht von über 60000 in einer Menge von 0,01 bis 601ob vorzugsweise 0,1 bis 20/,, in Niederdruckpolyäthylen möglichst gleichmäßig einarbeitet. It has now been found that the susceptibility of low density polyethylene against stress corrosion cracking in salt water at 900 G to a very great extent can be reduced by adding high pressure polyethylene with a molecular weight over 40,000 in amounts from 1 to 20%, preferably from 3 to 9010, and butyl rubber with a molecular weight of over 60,000 in an amount of 0.01 to 60,000 preferably 0.1 to 20 / ,, incorporated into low-pressure polyethylene as evenly as possible.

Die auf diese Weise erzielbare Wirkung ist überraschend hoch. So kann z. B. durch Zugabe von 501, Hochdruckpolyäthylen mit einem Molekulargewicht von 44000 und 0,4°/0 Butylkautschuk, mit einem Molgewicht von über 60 000, die Spannungsrißbildung von Niederdruckpolyäthylen in Salzwasser bei 900 C von 2 Tagen auf 50 Tage und darüber hinausgeschoben werden. The effect that can be achieved in this way is surprisingly high. So can e.g. B. by adding 501, high pressure polyethylene with a molecular weight of 44,000 and 0.4% butyl rubber, with a molecular weight of over 60,000, the formation of stress cracks of low-pressure polyethylene in salt water at 900 C from 2 days to 50 days and above be postponed.

Durch jeweilige Zugabe der Einzelbestandteile der Masse in der angegebenen Menge erreicht man dagegen nur geringfügige Vergütungen auf etwa 4 bis 8 Tage) woraus ersichtlich ist, daß erst durch Kombination der beiden Zusätze für die Technik interessante Wirkungen erreicht werden. Besonders hohe Vergütungen lassen sich bei Niederdruckpolyäthylen erreichen, deren Molekulargewicht über 90 000 liegt. Eine gleichmäßige Verteilung der Zusätze in dem Niederdruckpolyäthylen ist Voraussetzung für die Erzielung hoher Effekte. By adding the individual components of the mass in the specified Amount, on the other hand, only minor payments are made for about 4 to 8 days) it can be seen that only by combining the two additions are interesting for the technology Effects are achieved. Particularly high remuneration can be achieved with low-pressure polyethylene reach whose molecular weight is over 90,000. An even distribution the additives in the low-pressure polyethylene is a prerequisite for achieving higher Effects.

Die Spannungsrißkorrosion von Niederdruckpolyäthylen läßt sich durch Zusätze von Polyisobutylen oder Paraffinen natürlicher oder synthetischer Herkunft nur geringfügig vermindern. Man erreicht auch praktisch keine weitere Verbesserung durch Zugabe von Polyisobutylen oder Paraffinen zur erfindungsgemäßen Mischung von Niederdruckpolyäthylen, Hochdruckpolyäthylen und Butylkautschuk. The stress corrosion cracking of low-pressure polyethylene can pass through Additions of polyisobutylene or paraffins of natural or synthetic origin decrease only slightly. Practically no further improvement is achieved either by adding polyisobutylene or paraffins to the inventive mixture of Low pressure polyethylene, high pressure polyethylene and butyl rubber.

Durch Zugabe von für Niederdruckpolyäthylen geeigneten Stabilisierungsmitteln läßt sich eine weitere Steigerung der Vergütung erzielen, deren Höhe weitgehend von der Wirksamkeit des zugesetzten Stabilisierungsmittels abhängig ist. Besonders gute Wirkungen können beispielsweise durch zusätzliche Beimengungen von Schwefel, Mercaptobenzimidazol, Diphenyl-p-phenylendiamin, 4,4'-Dioxydiphenyl und Epoxyverbindungen beobachtet werden. Es sei in diesem Zusammenhang darauf hingewiesen, daß einige Stabilisatoren, wie besonders Schwefel und Di-fl-naphthyl-p-phenylen-diamin, bereits bei alleiniger Zugabe eine bemerkenswerte Vergütung im Sinne einer Herabsetzung der Spannungsrißkorrosion neben der in erster Linie gewünschten-Verbesserung der Alterungsbeständigkeit der Masse zeigen. By adding stabilizers suitable for low-pressure polyethylene a further increase in remuneration can be achieved, the amount of which is largely from the effectiveness of the stabilizing agent added is dependent. Particularly good ones Effects can, for example, through the addition of sulfur, mercaptobenzimidazole, Diphenyl-p-phenylenediamine, 4,4'-dioxydiphenyl and epoxy compounds can be observed. It should be noted in this connection that some stabilizers, such as especially sulfur and di-fl-naphthyl-p-phenylenediamine, even with sole Addition of a remarkable remuneration in the sense of a reduction of the stress corrosion cracking in addition to the primarily desired improvement in the aging resistance of the Show crowd.

Claims

Another advantage of this procedure is the fact that that the color and also the good electrical properties of the base material in the treatment used are retained. Fillers in an amount up to to 1001o and other additives such as dyes, antistatic agents and plasticizers the effectiveness of the additives used is generally only slightly.

According to the method described, the low-pressure method can also be used producible copolymers of ethylene with other olefins, such as propylene, Butylene and isobutylene, preferably those with a proportion of the second component of up to 600in as well as mixtures of polyolefins with one another with over 650 / o low-pressure polyethylene be remunerated. There is also a remuneration of masses, which is achieved by mixing Copolymers with mixtures of polyolefins are obtained on the above Way possible. The observed effect is sometimes considerably higher than that of Low pressure polyethylene detected.

For technology, the procedure described means in all cases a significant technical advance in which low-pressure polyethylene under Stress stress with water, in particular with warm or hot water or Steam, with wetting agents and / or solvents or mixtures of these substances comes into contact. The process is of particular importance in the case of low-pressure polyethylene sheathed cables, which are completely or partially laid under water, as tensions can never be avoided here. Even with pipes, especially those with larger diameters, which with extrusion presses (see e.g.

G. Schenkel, Kunststoffe, 45 [1955], pp. 486 to 490; G. Schulz and K. Mehnert, Kunststoffe, 45 [1955], p. 590) by welding plates or by centrifugal casting (see e.g. 5th branch, Modern Plastics, September 1955, Pp. 123 to 133; M. S. Welling, Plastics, August 1956, pp. 194 to 197) on pressed parts and on metal surfaces Protective layers, the coating described can bring significant advantages, depending according to how strong the voltage and temperature stresses are, which on burden these parts.

For injection molded parts that are used under water or with Salt water or wetting agents can come into contact at higher temperatures described procedures may be decisive for a possible use be of low pressure polyethylene. Also for after the deep drawing process (see e.g.

H. Behringer, Kunststoffe, 45, p. 178 [1955]) produced objects and for liquid packaging in foils, using the method described Masses are made available that largely meet the respective requirements will.

Example 1 Powdered low-pressure polyethylene with a medium Molecular weight of 110,000 is on a roller heated to 145 "C in 1 to 2 Minutes stripped into a fur. 501, granulated high-pressure polyethylene are added to this skin with an average molecular weight of 42,000, 0.5 0 / o butyl rubber with a Molecular weight of over 60,000 and 0.1 01o sulfur added, roll in for 6 minutes thorough mixing of the fur further, the fur finally pulls off and cuts it into strips, which are then granulated in a suitable machine. These granules are fed into a screw press heated to 230 ° C., with a plastic layer 1.55 mm thick on a 1.5 mm thick copper wire a method customary in the art. From this coated wire you make curls around the single diameter and subject them to a heat treatment in salt water or sea water of 90 ° C.

It is found that the cable curls obtained in this way (A cable lock is a wire test piece with a Wrapping a cylindrical mandrel three or four times creates a wire helix will) need 60 days for cracking to occur, while cable curls, which from the The same product has been manufactured in the same way without the additives mentioned show cracking in as little as 1 to 3 days. It is understandable that the test conditions described for the technology are extremely harsh conditions, but which allow differences to be determined in a short time.

Example 2 A powdered copolymer from Molecular weight 130,000, which consists of polymerizing a gas mixture from 980/0 ethylene and 20 / o propylene, obtained by a low pressure process was carefully mixed with 0.5% powdery polypropylene in a high-speed stirrer of molecular weight 200,000, which is produced by a low pressure process 0.1% mercaptobenzimidazole and 1.3% carbon black of one particle size by 30, the mixture rolled on a roller heated to 145O C while at the same time Addition of 3.5 dz, high-pressure polyethylene granules with a molecular weight of 46,000 and 0.25 0 / o butyl rubber with a molecular weight of over 60,000 to form a skin this carefully for 7 minutes on the roller and then peel it off. To Before cutting up the warm fur, the strips are made into granules with which one can produce a 2 mm thick on a screw press at a maximum of 225C C Sheathed copper wire 2 mm thick. You hang curls from this 6 mm thick cable around its own diameter in salt or sea water of 90 "C and compares it with Curls from cables which, without the additives mentioned, only consist of the copolymer have been produced in the same way, it is found that in the case of the latter cracking occurs after about 5 days while the curls emerge from the mass, which has been remunerated according to the procedure described, only after about 90 days reveal cracking.

PATENT CLAIMS: 1. Method for reducing stress corrosion cracking of polyethylene or copolymers of ethylene with other olefins, which after Low pressure polymerization processes had been produced, and / or their Mixtures with other polyolefins produced by low pressure processes, thereby characterized in that one is prepared in the low-pressure polymerization process Polymers, Copolymers or polymer mixtures 1 to 20 percent by weight, preferably 3 to 9 percent by weight of high pressure polyethylene with a molecular weight above 40,000 and at the same time 0.01 to 6 percent by weight, preferably 0.1 to 2 percent by weight Butyl rubber with a molecular weight of over 60,000 and, if necessary, for low-pressure olefin polymers effective stabilizers or other remuneration agents in themselves better known Way with as evenly a distribution of the additives as possible.

2. The method according to claim 1, characterized in that as Compensating agents, fillers, dyes, antistatic agents and plasticizers are used.

Documents considered: Chemical Trade Journal, Vol. 135, 1954, pp. 1694 to 1695.