DD291770A5 - METHOD FOR PRODUCING POLYETHYLENE MOLDING FOR PROFILES - Google Patents

Abstract

The invention relates to a process for the preparation of polyethylene molding compounds for profiles. The aim of the invention is to increase the utility value characteristics of profiles or pipes. The increase in creep rupture strength is achieved by using {polyethylene molding compound; profiles; Tube; Creep strength; Low density polyethylene; Ruszbatch; Waermestabilisator; Silicic acid, micronised, hydrated}

Description

Field of application of the invention

The invention relates to the production of improved polyethylene molding compounds for profiles, preferably for pipes.

Characteristic of the known state of the art

The manufacture and use of plastic pipes, e.g. PVC, polystyrene, low or high density polyethylene is known and has long been used commercially. Two quality criteria are essential, the creep strength, which is determined by the material, and the tolerances which depend on the material and the processing conditions.

It is known for the production of pipes u. a. Use low-density polyethylene. Such mixtures and a method of making these compositions are e.g. known from DE-PS 1226782.

For reasons of processability and to obtain not too rigid pipes, which are difficult to install, especially when used as water pipes, one usually chooses a polyethylene material with densities between 0.920 and 0.925 g / cm ³ and a melt index between 0.3 and 1.0 g / 10min at 190 ° C off. To stabilize the material, the polyethylene is dyed black with carbon black and additionally mixed with conventional stabilizers. Dyeing is usually done by preparing a polyethylene-carbon black mixture with carbon black concentrates between 5 and 50 wt.% By weight and incorporating this carbon black concentrate into a larger amount of polyethylene in the usual manner using kneaders, rolling mills, screw extruders or disk kneaders, and optionally a stream of molten polyethylene. It is usually used so much carbon black concentrate that contained in the resulting molding material for pipes 1 to 10 parts by mass in% carbon black. As carbon black, the usual Pußsorton, especially Gasruß and furnace black, have proven.

However, it has been shown that the creep strength of such mixtures is very often not sufficient after processing into tubes and that there are spray holes, which then lead to leaks and cracks to the point of uselessness.

The creep rupture strength of polyethylene pipes can be increased according to DE-OS 27410OS or EP-PS 0001110, if the base material used for the batch is an ethylene copolymer with 5 to 50 parts by mass in% carboxylic acid ester.

In this case, the concentrate contains 5 to 50 parts by weight in percent carbon black of the particle size 5 to 70 pm and 0 to 5 parts by mass in% of a stabilizer. The batch content in the final product is between 5 and 30% by weight in%. Compared to the use of an ethylene homopolymer as a batch material results in a significantly higher creep strength. A disadvantage, however, is that the cost of stocking the different starting polymer increases, the price of the ethylene-carboxylic acid ester copolymers over that for polyethylene, a change in the Grundoigenschaften of the polyethylene takes place and the ethylene-carboxylic acid ester Copoiymeren in alkaline Madien (inside like outside) are slowly being implemented and their properties change.

It is also known to use various matrix materials for the carbon black, e.g. to DE-OS 2603378 polymer powder with a certain particle size, according to US-PS 2 512 459 and GB-PS 890426 low molecular weight waxes or according to DD-PS 257 440 a polyethylene with respect to the base material to 60000 to 120000g / mol reduced molecular weight.

Furthermore, it is known that certain improvements can be achieved by modifying the carbon black (SU-PS 71/099, SU-PS 709639, SU-PS 697533, SU-PS 763397) or the polyethylene crosslinked (DE-OS 2164560, JP -PS 83-38727).

The previously disclosed molding compositions based on mixtures of polyethylene as a base material and carbon black batch with polyethylene as a batch material show the disadvantage of insufficient creep strength. Laying the pipes underground for drinking water pipes increases the risk of developing so-called "spray holes", which then eventually pass into slots and render the pipe unusable.

Aim of the invention

The aim of the invention is to increase the Gebrouchswortelgenschaften, especially the creep strength, of profiles or pipes based on low density polyethylene.

Explanation of the essence of the invention

It was an object to produce such a soot-containing Polyothylenformmasse., Which gives the profiles or tubes produced therefrom an improved Zeitstandsfostigkoit without other positive properties of the polyethylene base material are changed.

The object is achieved by a process for the production of polyethylene molding compounds for profiles, preferably for pipes which consist of low-density polyethylene into which a soot-containing polyethylone batch has been incorporated by producing a homogeneous molding composition according to the invention, from A) 84.36 to 95, 75% by weight of polyethylene with a density of 0.918 to 0.922 g / cm ^? and a melt index at 463K and 21.19N load from 0.1 to 0.5g / 10min, B) 4 to 15% by weight of a carbon black batch consisting of 80 to 60 parts by weight in% of a polyethylene having a density of 0.914 to 0.922 g / cm ³ and a melt index at 463K and 21.19N loading of 0.1 to 8, J g / 10 min and 20 to 50 mass% of carbon black, C) 0.2 to 0.5 mass% of micronized, hydrated silica and D) 0.05 to 0.15 mass% of a conventional heat stabilizer.

As micronized, hydrated silica products are used, such as those of the VEB Chemische Werke Fährbrücke, for example, "Suprasil", which is further characterized in that it has an average water vapor absorption of 41.9 mg / g at a specific surface area of about 149m ² / g measured by the BET method. As thermal stabilizers, compounds such as 4,4-thlo-bis (6-tert-butyl-m-cresol) or possibly also tetrakis (methylene-3) 3 'are used. 5'-di-tert-butyl-4-hydroxyphenyl / -proplonat) methane.

Preferably, the preparation of the molding composition by the micronized, hydrated silica (C) of the component A is added and then the components D and B are fed.

A further advantageous embodiment of the method is that after mixing A with B and D, the component C is added.

It is likewise advantageous to add components C and D to component B and then to carry out intimate mixing with A.

Surprisingly, the disadvantages of the known molding compositions can be avoided.

There is no soot agglomeration and the distribution of the carbon black in the polyethylene base is good. The Zoitstandsfestigkeit can be significantly increased.

The invention will be explained in more detail with reference to the following embodiments.

AusfOhrungsbelsplela

Example 1 (comparative example)

On a conventional Busskneter a Rußbatch was prepared from 25 parts by mass in% carbon black, 0.5 parts by mass in% of the stabilizer 4,4-thio-bis (6-t-butyl-m-krosol) and a polyethylene having a density of 0.920g / cm ³ and the melt index of 0.3g / 10m! n at 463K and 21.19N load. 10 parts by mass in% of this batch were then mixed homogeneously with 90 parts by mass in% polyethylene with the density 0.920 g / cm ³ and the melt index of 0.3 g / 10 min at 463 K and 21.19 N load on a twin-screw extruder and processed into granules

 The suitability as a pipe material was checked as follows:

On a laboratory extruder (Brabender-Plasticorder, 25D) a tube with the outside diameter of 16mm and a wall thickness of 0.6mm is extruded and cooled in air (295 ± 4K). 5 sections of 800 mm each of this tube are filled with water and suspended in a water bath with the temperature of 353 K. The hose ends are connected airtight with an apparatus, which pressurizes the hose contents with compressed air at a constant pressure of 100 kPa. The average service life up to the occurrence of defects in the hose jacket (spray hole, crack, burst break, etc.) is assessed. The individual results are given in the table.

Example 2 (comparative example)

On a conventional Busskneter soot batch was prepared from 40 parts by mass in% carbon black, 1.6 parts by mass in% of the stabilizer tetrakis (methylene-3/3 ', 5'-di-t-butyl-4-hydroxyphenyl / propionate) methane and a polyethylene having the Dichte0,915g / cm ³ and the melt index 7.0 g / 10 min at 463K and exposure N. 21.19 6% by mass of this batch are 94 parts by mass in% of polyethylene with a density of 0,920g / cm ³ and the melt index 0.3 g / 10 min at 463 K and 21.19 N N the sample homogeneously mixed on a twin-screw extruder and processed into granules.

Example 3

Analogously to the comparative examples, a carbon black batch was prepared on a Busskneter from 25 parts by mass in% carbon black, 0.5 parts by mass in% 4,4-thio-bis (6-tert-butyl-m-cresol), 2 parts by mass in% mikronisiertor, hydrated silica and a polyethylene having a density of 0.920 g / cm ³ and a melt index of 0.3 g / 10 min at 463 K and 21.19 N load. This batch was added to a twin-screw extruder in an amount of 10 parts by weight in% of a 0.920 g / cm ³ density polyethylene melt having a melt index of 0.3 g / 10 min at 463 K and a load of 21.19 N.

Example 4

A carbon black batch prepared from 20 parts by mass in% of carbon black, 0.34 parts by mass in% of 4,4-thlobis (6-t-butyl-m-cresol), 3.4 parts by mass in%, analogous to the Vorstellsbolsplelon on a Buaskneter micronised, hydrated silicic acid and a polyethylene having a density of 0.922 g / cm ³ and a melt index of 0.1 g / 10mln at 4Θ3Κ and 21.19N load. This batch was mixed in a mass of 15% by mass with a polyethylene of density 0.918 g / l OmInn and with the melt index of 0.5 g / 10 ml at 463 K and 21.19 N load on a twin-screw extruder.

Example 5

On a Bussknoter was a soot batch of BO mass fractions in% carbon black, 3.75 parts by mass in% TetraklB (methylene-3- / 3 ', 5'-dl-tert-butyl ^ -hydroxyphenylZ-proplonatlmethan and a polyethylene of density 0.914g / cm ³ and with the melt index of 8.0 g / 10 min at 463 K and 21.19 N. This batch was made in an amount of 4 parts by mass in% of a polyethylene melt with a density of 0.922 g / cm ³ and a melt index of 0.1 g / 10min at 463K and load of 21.19N in a twin-screw extruder and intimately mixed with it The addition of 0.3 parts by weight in% micronised, hydrated silica is carried out separately by direct dosing into the melt.

Examples

On a twin-screw extruder, a polyethylene of density 0.920 g / cm ³ and melt index of 0.3 g / 10 min at 463 K and 21.19 N load of 0.3 wt% in micronized, hydrated silica was intimately mixed and granulated. This granulate was remelted on a twin-screw extruder and treated with a carbon black batch consisting of 40% by weight in% carbon black, 1.6% by mass in% tetrakis (methylene-3-A3 ', 5'-di-tert-butyl-4-hydroxyphenyl / Propionatlmethan and a polyethylene of density 0.916g / cm ³ and with the melt index of 6.0g / 10min at 463K and 21.19N load mixed.

Example 7

On a Buss kneader, a carbon black batch of 40 mass% of carbon black, 1.6 mass% of tetrakis (methylene-3- / 3 ', 5'-di-tert-butyl-4-hydroxy-phenyl / -propionate) methane, 5 parts by mass in % micronized, hydrated silica and a polyethylene of density 0.916g / cm ³ and having the melt index of 6.0g / 10min at 463K and 21.19N load. 6 parts by mass in% of this batch were homogeneously mixed on a twin-screw extruder with a polyethylene of density 0.920 g / cm ³ and with the melt index of 0.3 g / 10 min at 463 K and 21.19 N load.

table

Example test result, average service life

No. of5lone3sungonin (h)

1 5

2 7

3 54

4 38

5 49

6 50

7 62

Claims (4)

1. A process for the preparation of polyethylene molding compositions for profiles, preferably for pipes, which consist of a low density polyethylene, in which a soot-containing polyethylene batch has been incorporated, characterized in that from a mixture of A) 84.35 to 95.75 parts by weight in% of polyethylene having a density of 0.918 to 0.922 g / cm ³ and a melt index of 0.1 to 0.5 g / 10 min at 463 K and 21.19 N load, B) 4 to 15 parts by mass in% of a carbon black batch, consisting of 'a) 80 to 50 parts by weight in% of a polyethylene having a density of 0.914 to 0.922 g / cm ³ and a melt index of 0.1 to 8.0 g / 10 min at 463 K and 21.19 N load, and b) 20 to 50 mass parts in% of carbon black, C) 0.2 to 0.5 parts by weight in% of micronised, hydrated silica and D) 0.05 to 0.15 parts by mass in% of a conventional heat stabilizer a homogeneous molding composition is prepared. 2. The method according to claim 1, characterized in that the micronized, hydrated silica (C) of the component A is added and then the components D and B are fed. 3. The method according to claim 1, characterized in that after mixing of A with B and D, the component C is added. 4. The method according to claim 1, characterized in that the component B, the components C and D are added and then an intimate mixing with A takes place.