DE1190178B - Process for crosslinking ethylene polymers - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY Int. Cl .:

C08f

GERMAN

PATENT OFFICE

EDITORIAL

German: 39 b -22/06

Number:
File number:
Registration date:
Display day:

1190178
G38175IVc / 39b
November 10, 1960
April 1, 1965

The invention relates to a method for crosslinking ethylene polymers by the action of a new one Class of peroxides at temperatures above the softening point of the polymer.

Ethylene polymers such as those disclosed in U.S. Patents 2,153,553 and 2,816,883 are general known and by their solubility in organic solvents and their thermoplastic properties marked. It is also known the solubility and thermoplastic character of the Reduce polymers by crosslinking, for example by irradiating the polymer with electrons or by adding radical-forming substances.

For the crosslinking of polymers by radical-forming substances have hitherto mainly organic peroxides are used. Although numerous organic peroxides are a crosslinking of ethylene polymers cause, the majority of such compounds show considerable disadvantages.

Benzoyl peroxide, for example, is extremely dangerous at the required mixing temperature because of its tendency to decompose explosively. At the admixing temperature to the polymer, other peroxides show a half-life which is insufficient to achieve uniform crosslinking. Many other peroxides already have a high rate of decomposition at the softening point of the polymer, so that they crosslink the polymer so quickly and strongly that the subsequent processing steps are hindered or made impossible. This applies in particular to high-density polyethylenes, which can be produced, for example, according to US Pat. No. 2,816,883 and have a melting point of 127 ^° C. or above. There is therefore a lack of suitable crosslinking agents for high-density polyethylene, which can be added to the polymer prior to shaping without causing a degree of crosslinking that hinders processing during the heating above the softening point, which is necessary for deformation, but only leads to crosslinking at an even higher temperature .

From USA. Patent 2916481 a process for crosslinking polyethylene is known, wherein the polymer with 0.1 to 10% of an α, ω-bis (tert -. Alkylperoxy) - κ, κω, ω - tetraalkylhexans or butane is heated. However, this process has the significant disadvantage that the bis-peroxides used cause premature, partial crosslinking of the polymer even at low processing temperatures, which leads to an undesirable increase in viscosity during extrusion and, in parallel, processes for crosslinking ethylene polymers

Applicant:

W. R. Grace & Co., New York, N.Y. (V. St. A.)

Representative:

Dr. rer. nat. J.-D. Mr. v. Uexküll, patent attorney, Hamburg-Hochkamp, Königgrätzstr. 8th

Named as inventor:
Razmic Sarkies Gregorian,
Silver Spring, Md. (V. St. A.)

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a correspondingly increased power requirement occurs in the extruder. This not only wears out the processing machines excessively, but also frequently Caused a complete blockage of the machines, which completely dismantled them and several hours are lost for processing.

It has now been found that these disadvantages are avoided by using bis-peroxides, in which the carbon atoms carrying the peroxy groups have hydrogen atoms.

Accordingly, according to the present invention, the process for crosslinking ethylene polymers is accomplished Heating the polymer with a bis-peroxide to a temperature above its softening point characterized in that the polymer with 0.001 to 10 percent by weight of a bis-peroxide general formula:

R HH R

_R '_C - O - O - C - X - C - O - O - C - R'

heated, wherein X is a polymethylene group, R is alkyl groups and R 'represents aryl or alkyl groups.

The process according to the invention using the bis-peroxides described gives highly crosslinked Polymers with improved clarity and low tendency to stress cracking, such as in that Example is shown in more detail.

The bis-peroxides used according to the invention can be used to crosslink polyethylene with a Density of about 0.92 to 0.96 can be used; H. thus for high and low density polyethylene. To the Crosslinking of ethylene polymers according to the invention

509 537/464

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according to the method are only relatively low for purposes in which polyethylenes with low Quantities of bis-peroxide required. Based on the tendency to stress cracking and improved Weight of polyethylene is an additive of 0.001 to be needed for clarity. The crosslinked polymers 10.0 weight percent is useful, although an additive also has greater dimensional stability and

from 0.001 to 0.5 weight percent is preferred. 5 Solvent resistance at low and increased

According to the method according to the invention, the temperatures.

Ethylene polymers with a bis-peroxide according to The following example illustrates the invention. above formula mixed and by heating, In the example, the melt index was preferably cross-linked to a temperature above the ASTMD-1238-52T and the density of the polymer in the softening point of the polymer. For this purpose io a density gradient according to the up to 200 ⁰ C and above Laboratories proposed by Bell, temperatures ASTM procedure to be applied as long as the heat decomposition of the density measurement at a fixed plastics by the polymers which are measured by the temperature and the density gradient.
Depends on the heating time, does not interfere. For mixing the reactants and the low density polyethylene of about 0.92, the preferred temperature range for the crosslinking example, unless otherwise stated, is 100 to 200 ⁰ C, while high density polyethylene is used to determine the degree of crosslinking Brabender Plastograph, model PL-V2, with a Vorvon about 0.96, preferably at 150 to 200 ⁰ C comparable device for recording Drehmomentsverändenetzt is. The polymer can first be brought to reaction temperature 20 from 0 to 1000 units, corresponding to a rotation, and then mixed with the bis-peroxide moment from 0 to 1 mkg possessed. This area could be. Instead, the polymer and, if necessary, by additional weights, can be increased to 0 to the bis-peroxide below its decomposition 5000 units, mixed according to a torque of temperature and then heated to 0 to 5 mkg. To be carried out. The bis-peroxide can, of course, of the invention, but other devices can also be added at temperatures below the softening point, for example a Banbury mixer or a point of the polymer, and used with this belt extrusion press.
be mixed. However, it is preferred to add the bis-peroxide to the molten polymer from the time of addition before decomposition to achieve a more uniform dispersion of the bis-peroxide to the molten polymer. To support the mixing up to the interruption of the crosslinking reaction, solvents for the bis-peroxide can be used, the torque increase shown as an example (Αγ) in narrow evidence benzene. If that's pardon. The greater the crosslinking, the greater the mixing below the decomposition temperature of the polymer, and the greater the bis-peroxide, the resulting mixture. The polygraph with constant speed of rotation mere can be operated before or at the same time as the crosslinking in. Any desired shape that can be achieved according to the invention, for example degree of wetting, is only limited by the performance using an extruder provided with a shaped outlet of the mixer with regard to the crosslinking opening, which is limited to a rise in torque caused. At a temperature above the softening point of the poly- dem process according to the invention, polymers can therefore be heated. ethylene, if desired, under controlled conditions The bis-peroxides used for the process according to the invention with an available suitable ausbaren bis-peroxides can be completely crosslinked after known retrofitting.
drive to be made. Primary, tertiary bis-per- 45 Another control of the degree of crosslinking oxides of the formula: provides the decrease in the melt index during the RR crosslinking of the polyethylene. Since the melting] j index varies inversely with the viscosity which ■ Q 'r η η rn γ γίι no r R' in turn directly conform to the degree of crosslinking rejuvenation aa _{5o] au} f _{t j zei} g _{t eme} decrease in Schmelzmdex that a 'Networking has taken place.

^KR In the example below, all are partial or

wherein X is a polymethylene group, R is an alkyl percentage by weight:

group and R 'represents an alkyl or phenyl group. . ,

represents, can preferably according to the basic procedure 55 example

U.S. Patent 2,403,709. 38 g of commercially available polyethylene granules from

The melt index 0.7 and a density of 0.96 according to the method according to the invention were in

Provided crosslinked ethylene polymers can be used for a Brabender-PIastograph kept at 170 ° C

Numerous uses can be used, for incorporated, and after a mixing time of 10 minutes

the polyethylene was previously used. The inventions for melting the polymer were 0.63 mmol

According to manufactured products are particularly suitable l, 10-bis- (tert-butylperoxy) -n-decane of the formula:

CH ₃ CH ₃
CH ₈ -C -O-O-CH ₂ - (CH _{2 ) 8} -CH 2 -OOC-CH ₃

CH ₈ CH ₂

added and mixing continued for an additional 10 minutes. From the time the bis-peroxide was added a torque increase of 200 units was recorded by the time mixing was complete.

Subsequently, the same experiment was repeated in the plastograph at a mixing temperature of 200 ⁰ C and up to the completion of mixing, a torque increase of 940 units recorded from the time of addition of the bis-peroxide.

From the above information it can be seen that the bis-peroxides used according to the invention are suitable for crosslinking ethylene polymers. In addition, the large difference in the increase in torque at 170 and 200 ^° C. shows that when the polymer is heated to 170 ^° C., only a relatively small amount of crosslinking occurs. In this way it is possible, by the process according to the invention, to deform ethylene polymers by heating to a temperature above their softening point and to bring about extensive crosslinking of the deformed polymer by subsequent further heating.

Comparative experiment

The procedure of the example was repeated, but now using a bis-peroxide as an example. -dimethyl-2,7-bis 2,7 (tert-butylperoxy) octane was used at mixing temperatures of 170 and 200 ⁰ C according to the USA. Patent 2,916,481. From the time of addition of the bis-peroxide to the reaction mixture until the termination of the mixing, an increase in torque was of 950 units, and with a mixing Tempe temperature of 200 ⁰ C, a torque increase of 980 units recorded at a mixing temperature of 170 ⁰ C. It can therefore be seen that with one of the USA. Patent 2,916,481 both of substantially the same degree of crosslinking is achieved bis-peroxide according to at 17O ⁰ C and at 200 ° C. Since the extruder temperatures commonly used in the extrusion of ethylene polymers between 170 and 200 ⁰ C., with the higher temperature is preferred, it is not by the method of USA. Patent 2,916,481 possible to preheat the next mixture to be extruded to the extrusion temperature without any substantial networking occurring.

Claims (2)

Patent claims: 1. A method for crosslinking ethylene polymers by heating the polymer with a Bis-peroxide to a temperature above its softening point, characterized in that that the polymer with 0.001 to 10 percent by weight of a bis-peroxide of the formula: R'— C — O — O — C — X — C — O — O — C — R ' R HH R heated, wherein X is a polymethylene group, R is alkyl groups and R 'represents aryl or alkyl groups. 2. The method according to claim 1, characterized in that that the polymer is deformed before or simultaneously with the crosslinking. 509 537/464 3.65 © Bundesdruckerei Berlin