DD268963A1 - POLYETHYLENE MOLDING FOR HALVES WITH IMPROVED PROPERTIES - Google Patents

Abstract

The invention relates to polyethylene molding compositions of 95 to 40 wt .-% low density polyethylene, 60 to 5 wt .-% high density polyethylene and 60 to 5 wt .-% of a copolymer of ethylene and α-olefin, for the production of semi-finished products with higher stiffness, good aging resistance and high resistance to shock-like loading are suitable. The application possibilities of the invention are preferably in the field of packaging and covering films, cable insulation as well as sprayed and blown hollow bodies.

Description

Field of application of the invention

The invention relates to polyethylene molding compositions which are suitable for the production of semi-finished products with higher rigidity, improved aging resistance and higher resistance to shock-like loads. These semi-finished products can include foils, cable insulation as well as molded and blown hollow bodies.

Characteristic of the known technical solutions

Blends of low-density polyethylene and high-density polyethylene are used for a variety of applications in the film and cable sectors. Of advantage here are the good processability on the conventional processing machines as well as the special field of use adaptable mechanical properties by mixing other components such as ethylene-vinyl acetate copolymers (DD-PS 140095), plasticizer (DD-PS 141427), polypropylene (DE AS 1719252), polyethylene glycol (DE-OS 2729433) can be improved.

It is found, however, that under use conditions, blends containing about one weight percent of high density polyethylene have a large decrease in scummocking stress and elongation after heat aging over low density polyethylene based feeds. These property changes severely limit the applicability of such mixtures.

Object of the invention

The aim of the invention is to develop polyethylene molding compositions for the production of semi-finished products, which are characterized by higher rigidity, good aging resistance and high resistance to shock-like stress.

Explanation of the nature of the invention

The invention has for its object to improve the compatibility of high density polyethylene and low density polyethylene in polyethylene molding compositions, so that with good processability, the characteristics of the molding compositions are above the characteristics eier Ausgangsskomponentf η. This object is achieved by polyethylene molding compositions for calf with improved properties of low density polyethylene and high density polyethylene and optionally known additives such as stabilizers, lubricants and anti-caking agents, propellant, according to the invention, the molding compositions 95 to 40Gew .-%, preferably 65 to 50Gew %, of a low-density polyethylene, 60 to 5% by weight, preferably 40 to 10% by weight, of a high-density polyethylene and 60 to 25% by weight, preferably 40 to 5% by weight, of a copolymer of ethylene and a Olefins and optionally 0.05 to 0.5% by weight, preferably 0.1 to 0.25% by weight, of a heat stabilizer and 0.5 to 3% by weight of a blowing agent.

The molding compositions advantageously comprise copolymers of ethylene and butene-1, hexene-1, octene-1 or a mixture of these monomers having a molecular weight distribution width <4 (ratio of weight average to number average molecular weight minus 1) and non-statistically distributed short chain branching.

As low-density polyethylene products can be used, which are prepared by free-radical polymerization in a stirred or tubular reactor and have a melt index of 0.15 to 5 dg / min and a density of 0.918 to 0.925 g / cm ³ . Suitable high density polyethylene are products made by gas phase, solution or suspension polymerization which have a melt index of 0.2 to 5 dg / m in and a density of 0.940 to 0.965 g / cm ³ . The copolymers of ethylene and olefins used advantageously have a melt index of 0.5 to 4 dg / min and a density of 0.918 to 0.930 g / cm ³ .

As copolymers of ethylene and α-olefins, wherein as α-olefins butene-1, hexene-1, octene-1 or mixtures of these α-olefins are used, products can be used by the high pressure process and gas phase, solution and suspension whose polymerization is carried out by catalytic, coordinative polymerization. The comonomer content is 2 to 10 mol%, preferably 5 to 8 mol%.

The molding compositions are prepared as a granule mixture or by mixing in the melt on known, advantageously continuously operating twin-screw extrusion plants. In this case, the components can be premixed by circulation in a high-speed mixer or storage bunker or fed via metering according to their weight or volume fraction of the feeder of the extruder. The mixing of the components can take place in a separate compounding process or directly during processing into a semi-finished product.

Auiführungsbelsplele example 1 Made of a low-density polyethylene with a melt index of 0.3 dg / min and a density of 0.921 g / cm ³ , a High-density polyethylene with a melt index of 0.5 dg / min and a density of 0.950 g / cm ³ and a copolymer

From ethylene and butene-1 having a melt index of 1 dg / min and a density of 0.920 g / cm ³ , the following mixtures are prepared as a compound or granule mixture. As a comparison, mixtures according to Comparative Examples 1 to 4 are prepared,

Table 1: Composition in% by weight PE-ND Ethylene-butene-1 Remarks PE-ND copolymer Examples - - - 100 100 - - 1 (comparison) - 35 - melt 2 (comparison) 65 mixture 3 (comparison) - 35 granules 65 mixture 4 (comparison) 10 40 melt 50 mixture example 1 15 30 melt ^ 55 mixture Example 2 20 15 melt 65 mixture Example 3 15 30 granules 55 mixture Example 4 35 15 melt 50 mixture Example 5

From Comparative Examples 1 to 4 and the novel molding materials Examples 1 to 5, 150 μm films were produced on a blown film line under the following processing conditions: Extruder: screw diameter D = 36 mm

Screw length 25D

Compression ratio 1: 3.5 Tool: Tool diameter 90 mm

Gap width 0.8 mm

Temperature range from 15O ⁰ C in the intake rising to 190 "C in the tool, blow-up ratio 1: 2

The characteristics of the starting materials and the films were determined by the following test methods: Density TGL14075

Melt index TGL 20996 Tensile strength TGL 20783/25267 Elongation TGL25267 Shock resistance TGL 20798/1

Tear propagation resistance after the thigh test by determining the tear propagation force on a 1SO-μm film, which is cut in a defined way.

The determined film characteristics are listed in Table 2. The results show that a much higher shock resistance is achieved by dio molding compositions according to the invention (Examples 1 to 5) than that which was to be expected due to the shock resistance of the starting materials on the basis of the additivity of the properties.

Table 2: tensile strenght quar strain crosswise Tear strength crosswise shock resistance Examples along N / mm ¹ along % along N / mm g / mm N / mm ² 21 % 60 N / mm 55 21 23 450 340 65 300 3.5 1 (comparison) 32 24 730 650 130 130 0.6 2 (comparison) 27 26 600 700 110 130 1.6 3 (comparison) 28 27 600 690 110 190 3.5 4 (comparison) 27 26 660 680 140 180 4.8 example 1 27 25 640 660 120 160 5.2 example \ 25 26 620 700 120 170 5.0 example 26 24 680 680 120 160 5.4 Example 4 26 620th 120 5.0 Examples

Example 2

The mixtures of Comparative Example 3 and Example 5 according to Table 1 are mixed with the addition of 0.1 wt .-% of 4,4 'thio-bis-3 tert-methyl-6-tert.butylphenol as a stabilizer on a twin-screw extruder and then granulated. Thereafter, dt η produced from the granules according to TGL 29979/03 at 200 ⁰ C press plates and determined on punched rod according to TGL14070 the tensile strength and elongation before and after heat aging, the shoulder rods of dimensions 115 χ 6 χ 2mm at 100 ° C 240h conditioned become. The characteristic values of Comparative Example 3 and the mixture according to Example 5 are shown in Table 3.

Table 3 example

3 (comparison) 5

Tensile strength N / mm ¹ Elongation%

Heat aging heat aging

before after

15.5 15 600 250

16.0 15.5 650 600

The high, substantially unchanged elongation value of the molding composition according to the invention after heat aging compared to the comparison mixture shows the improved aging resistance.

Claims (4)

1. Polyethylene molding compositions for semi-finished products with improved properties of low density polyethylene and high-density polyethylene and optionally known additives such as stabilizers, lubricants and anti-caking agents, blowing agents, characterized in that the molding compositions 95 to 40Gew .-%, preferably 65 to 50Gew. % of a low-density polyethylene, 60 to 5% by weight, preferably 40 to 10% by weight, of a high-density polyethylene and 60 to 5% by weight, preferably 40 to 5% by weight, of a copolymer of ethylene and α-olefins and optionally 0.05 to 0.5% by weight, preferably 0.1 to 0.25% by weight, of a heat stabilizer and 0.5 to 3% by weight of a blowing agent. 2. Polyethylene molding compositions according to claim 1, characterized in that the molding compositions copolymers of ethylene and butene-1, hexene-1, octene-1 or a mixture of these monomers having a comonomer content of 2 to 10 mol .-%, preferably 5 to 8 mol. -%, contain. 3. Polyethylene molding compositions according to claim 1, characterized in that copolymers of ethylene and butene-1, hexene-1, octene-1 or a mixture of these monomers having a molecular weight distribution width <4 (ratio of weight average to number average molecular weight minus 1) and not statistically distributed short chain branches are included. 4. Polyethylene molding compositions according to claim 1, characterized in that the molding compositions low-density polyethylene having a melt index of 0.15 to 5dg / min and a density of 0.918 to 0.925 g / cm ³ , high density polyethylene with a melt index of 0, 2 to 5dg / min and a density of 0.940 to 0.965g / cm ³ and copolymers of ethylene and α-olefins having a melt index of 0.5 to 4dg / min and a density of 0.918 to 0.930g / cm ³ included.