DE2354529A1 - Polyethylene contg. homogeneously distributed additives - by high speed mixing of liquid additives with heated resin - Google Patents

Abstract

Prodn. of polyethylene contg. homogeneously distributed cross-linking aids and/or antioxidants comprises heating polyethylene granulate to 85-95 degrees C in a fluid mixer at a high level of revs. per min., adding the additives in liquid form, then further heating up to 110 degrees C, and finally cooling immediately to 70 degrees C with further stirring. A suitable cross-linking aid is triallyl cyanurate (TAC) and pref. antioxidants are aromatic amines, phenols or organic phosphites. By using the mixer at about 3000 rpm the additives are worked into the granulated resin bodies without the surface becoming greasy or moist. Amts. up to 5% TAC can be added. Using liq. TAC mixed with highly dispersed silicic acid in ratio of 2:1, then 10% TAC can be worked in. If antioxidant is added simultaneously in ratio 1:1 then only a max. of 4% TAC can be added without effecting processing props. Cross-linked polyethylene is useful as insulation, for electric cables. The method gives homogeneous distribution of additives at low concn. as can be demonstrated by the even distribution of a slightly coloured additive.

Description

Dr. Fred Schimke Berlin, the 2 _O 7. 1975

Frank Heil

Process for the production of polyethylene containing additives

The invention relates to a method of manufacture of polyethylene, which contains additives, in particular antioxidants and / or crosslinking aids.

Polyethylene in cross-linked form is used as insulation electrical conductor twisting · To increase the crosslinking yield when exposed to high-energy rays or organic peroxides and heat Polyfunctional monomers incorporated into the polyethylene. To protect the polymer against degradation Effect of oxygen and ozone at high temperatures, antioxidants are added.

Ts iallyloyanurate (TAG) is predominantly used as a crosslinking aid, while aromatic amines, phenols or organic phosphites are predominantly used as antioxidants «

Both types of additives are required because of their low level Content can be distributed very evenly in the polymer. This is usually achieved by using the in Granulate form present PE in the kneader and / or on the The roller is melted and the additives are mixed into the polymer in small doses. Afterward must be granulated again.

This approach has three disadvantages. There are great energies and long times for melting the PE to spend. Furthermore, it is difficult to achieve evenly incorporating the small amounts of additive, there hardly any accumulations of concentration that have once arisen are to be eliminated. Thirdly, because of the poor solubility of the additives in PE, it is very difficult to obtain the To bring in additives at all. Uur with corresponding "

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small doses over long periods of time, concentrations of up to approx. 1% can be achieved. The manufacture of masterbatches is completely excluded.

In addition, this process has the disadvantage that the products produced in this way cause dreaded exudation phenomena have and represent a greasy granulate, which on extruders only under strong reduction the output can be processed.

The purpose of the invention is to find a method according to which the incorporation of additives without any special effort can be made in polyethylene

The invention is based on the object of getting away from the complex kneading and / or folding technology and through a simpler process, without any special technical effort, good training and a good one to ensure uniform distribution of additives in the highest possible concentration in the polyethylene

According to the invention, commercially available PE granulate is heated to ^ 90 ° C in a fluid mixer at high speed of the stirrer, then the additional substance is added in liquid form and the mixture is stirred further until a temperature of ~ 110 ° 0 is reached. Connection
cooled and bottled,

door from ~ 110 ° 0. Then, while stirring, to 70 ⁰ O

The surprising thing about this procedure is that the additional substances are worked into the surface of the granules that have become elastic at the relatively high speeds of rotation of the mixing tool of 3,000 rpm in such a way that the surface is neither greasy nor damp; Addition of up to 5 % TAC is possible according to this procedure. If the liquefied TAG is mixed with highly dispersed silica in a ratio of 2: 1, 10 % TAG can still be incorporated into PE without a drop in performance during extrusion due to the greasy surface of the granules.

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Antioxidants are added at the same time as TAC, ^ so with a ratio lsi can in general only an amount of max. 4% without impairing the ■ processing properties of the PE granulate will.

The procedure shown makes it possible to use large quantities without great technological effort Bringing crosslinking aids and / or antioxidants. Which is particularly beneficial uniform distribution of the additives even with very low concentrations, as in the uniform color the granules are easily detectable when using slightly colored additives

The invention is intended to be based on an exemplary embodiment explained.

40 kg PE with a melt index MFi; 0.5 introduced in granulate form · At stirring speeds of 3,000 rpm, after reaching ~ 90 ° 0 2 kg of melted TAG are added. Stirring is continued until a temperature of HO ⁰ C is reached. It is then ^{cooled to 70 °} C. while stirring and the mixture is filled. The total cycle time is a <20 min. A dry granulate is obtained which contains the added crosslinker in an even distribution.

409884/0832

Claims (1)

Claim: Process for the production of polyethylene which contains crosslinking aids and / or antioxidants in uniformly distributed form, characterized in that polyethylene granules are heated in a fluid mixer at high speed of the mixing tool to 85 ⁰ - 95 ⁰ O, the additives are added in liquid form and then further heated to rwii0 ° 0 and then immediately cooled ^{to <70 0 O with further stirring.} 40 9 8 8 4/0832