CS210738B1 - A method for producing polypropylene and low density polyethylene wraps - Google Patents

Abstract

The invention relates to the production of blends of polypropylene and low density polyethylene for extrusion coating. The invention solves the radical degradation of polypropylene simultaneously with mixing with polyethylene, which is protected against crosslinking by initiators of radical degradation of polypropylene by synergistic crosslinking of phenolic, phosphite and sulfur stabilizers and granulation of the mixture in a single pass through the extruder.

Description

(54) The production method mixes polypropylene and low density polyethylene

The present invention relates to the production of blends of polypropylene and low density polyethylene for extrusion coating.

The invention solves the radical degradation of polypropylene simultaneously with mixing with polyethylene which is protected against crosslinking by the initiators of radical degradation of polypropylene by synergistic networks of phenolic, phosphite and sulfur stabilizers and granulation of the mixture in a single pass through the extruder.

The present invention relates to polypropylene and low density polyethylene compositions for extrusion coating technology. In particular, it relates to materials wherein polypropylene is the predominant component. Treatment of the material by extrusion coating, such as paper, fabric or metal foil, is a well-known technology in which the polymer or polymer blend is extruded to the treated material moving at a suitable speed below the extruder die. This technology is described in both textbooks and patent literature, such as British Patent Specifications 688 637 or 992 388.

This technological process is widely used to treat the material with low density polyethylene, where high surface quality (uniformity of deposit) and advantageous working speeds of movement of the substrate of up to 200 meters or more per minute are commonly achieved.

The use of polypropylene for the treatment of materials such as paper, textile or metal foil offers a number of advantages such as higher heat resistance, stiffness of the coating, lower permeability to water vapors and gases, resistance to fats and oils.

However, the technological process of extrusion coating of polypropylene is associated with a number of difficulties concerning both the transverse and longitudinal profile of the deposit, and does not allow the process efficiency common to low density polyethylene to be achieved.

The above problems can be overcome by using polypropylene-low density polyethylene mixtures. According to British patent specification no. No. 992,388, such blends can be prepared by coextrusion of a blend of polypropylene having a flow index of 20 to 80 g / 10 min. and low density polyethylene with a flow index of 4 to 20 g / 10 min.

However, this process requires to prepare a polypropylene having a sufficiently high flow index in advance, which is usually done by degrading polypropylene initiated by radical generating compounds such as organic peroxides.

Such degradation processes are widely described in patent literature, such as in Belgian patents 806 669 and 815 357, and Japanese patent 54-090 291 et al.

Low density polyethylene is commonly known as a polymer subject to the crosslinking process in the presence of radical initiators such as organic peroxides. Such reinforced proportions of material then cause technological difficulties in extrusion coating. Conversely, polypropylene in the presence of radical initiators such as organic peroxides is subject to degradation due to its chain structure, narrowing the molecular weight distribution and decreasing the number and weight average molecular weights.

Surprisingly, it has been found that when the polypropylene degradation process initiated by radical initiators, for example peroxides, is carried out in the presence of low-density polyethylene and in the presence of stabilizers, there is no strengthening of the polyethylene.

SUMMARY OF THE INVENTION The present invention provides a process for the production of extrusion coating compositions of polypropylene and low density polyethylene comprising 80 to 95% by weight polypropylene having a flow index reduced by radical degradation and 5 to 20% by weight low density polyethylene having a flow index of 2 to 70 g / 10 min. stabilizers and processing additives by extrusion, characterized in that a blend of powdered polypropylene having a flow index of 0.2 to 10 g / 10 min./230 ° C, 23 N / a and a low density polyethylene having a flow index of 2 to 70 g / 10 min. 190 ° C, 21.2 N / melt and linete at 150 to 300 ° C in the presence of 0.02 to 0.2 wt. % of organic peroxides and 0.1 to 0.6 wt. % of a synergistic blend of phenolocyte antioxidants, phosphites and sulfur antioxidants per 100 parts of a polyolefin blend.

Linear polypropylene has a flow index of 0.2 to 10 g / 10 min./230 ° C, 23 N according to CSN 640 861 / -3 and a density of 690 to 915 kg m. It is used in the form of powder directly from production. Low density sentences, w. ·

21073 Polyethylene has a flow index of 2 to 70 g / 10 min / 190 ° C, 21.2 N according to CSN 640 861 / and a density of -3

910 to 922 kg m. It can be used in the form of powder or granules.

The organic peroxides as radical sources are selected such that their half-life is 30 to 200 s at 230 ° C. For example, di-tert-butyl peroxide, 1,1-bis- (tert-butyl peroxy) -3,3,5 trimethylcyclohexane, dicumyl peroxide, tert-butyl perbenzoate or 2,5 dimethyl-2,5 di (tert-butyl peroxy) hexane, and both in their natural form and coated on a polymeric or inorganic carrier.

The stabilizers used in the preparation of said materials belong to the group of phenolic stabilizers, for example 1-hydroxy-2,6-di-tert-butyl-4-methylbenzene, 3-methyl-6-terobutylphenol, pentaerythritol-tetra-beta / 4-hydroxy-3,5 -di-tert-butylphenol / propionate etc. of sulfur secondary antioxidants such as dilauryl 3,3'-thiodipropionate, distearyl 3,3'-thiodipropionate, and phosphite stabilizers such as tris- (1'-phenyl-4-ethylphenyl) phosphite, tris- (1'-phenyl-4-nonyl) phosphite.

Calcium stearate is generally used as a processing additive to improve the flow properties of the polymer blend.

The use of synergistic mixtures of the aforementioned stabilizers then makes it possible to carry out peroxides-initiated degradation of polypropylene in the presence of low-density polyethylene without crosslinking the polyethylene component.

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The process for preparing said materials begins with mixing the polypropylene powder with peroxide and stabilizers and processing ingredients in a fluid mixer. Either a low-density polyethylene powder is added to the mixture thus prepared and the two components are again transferred to the above-mentioned apparatus, or granulated polyethylene is added directly to the kneading machine.

In the next step of the manufacturing process, either a blend of polypropylene and low density polyethylene prepared as described above is fed into the extruder, or polypropylene with peroxide and other additives prepared as above and a low density polyethylene granulate are co-metered.

For granulation, a single-screw or multi-screw extruder is used, equipped with a dosing device for dispensing powder or simultaneously powder and granulate. The single-screw machine is equipped with a mixing torpedo, the twin-screw machine is equipped with a kneading zone. Temperatures along the screws are adjustable both along the screw and on the head in the temperature range of 150 to 300 ° C. The residence time of the material in the machine is controlled by the screw speed. The granulation is carried out either on the string or on the head, the cooling medium being water at a temperature of 20 to 80 ° C.

The advantage of our process is that the degradation of polypropylene and its modification with low-density polyethylene are carried out in only one pass through the extruder, which provides significant savings in both energy and labor costs and other costs compared to previously used processes, because the polypropylene degradation operation is eliminated.

the examples below illustrate the process and working conditions in more detail. The parts shown in the examples are by weight. Parts of peroxide, stabilizers and processing additives are given relative to polypropylene (polypropylene = 100 parts), the weight fraction of low density polyethylene is based on the whole polymer fraction (polypropylene + polyethylene = 100 parts).

The melt indexes of IT polymers or mixtures thereof are determined as follows:

Polypropylene: 230 ° C, piston force 23 N.

Low density polyethylene: 190 ° C, piston force 21.2 N.

Polypropylene / low density polyethylene mixtures: 23 ° C, piston force 23 N.

Working procedure according to ČSN 640 861.

Example 1

100 parts of polypropylene powder with a flow index = 3.7 g / 10 min were placed in a fluid mixer. After starting the stirrer, 0.15 parts of phenolic stabilizer (2,6-di-tert-butyl-4-methylphenol), 0.2 parts of phosphite stabilizer Γtris- (1'-phenyl-4-ethylphenyl) phosphorous acid ester, 0.1% and 0.12 parts of peroxide [2,5-dimethyl-2,6- (di-tert-butylperoxy) hexane].

The mixture was stirred at 25 ° C for 45 minutes. Then 20 parts of low density polyethylene powder with a flow index = 20 g / 10 min were added. The mixture was stirred at the same temperature for 30 minutes. The resulting powder mixture was fed into a twin-screw extruder with a screw diameter of 53 mm and a length-to-screw ratio = 29, a kneading zone at a distance of 14 diameters from the hopper.

In four adjustable bands the following temperatures (from the hopper) were: 215, 230, 215 and 165. The extruder head temperature was 200 ° C. The screw speed was 80 rpm. The resulting polymer blend had a flow index = 38 g / 10 min.

The polymer blend was extruded from a slit die to a paper speed of 60-220 m / min. The polymer blend was 15 to 40 g / m < 2 > and was uniform in the longitudinal and transverse directions.

The narrowing of the melt curtain was 1.4 cm at each edge, while for polypropylene with a flow index = 40 g / 10 min. was 8 cm at each edge.

Example 2

The procedure was analogous to Example 1 except that 0.09 parts of peroxide initiator [2,5-dimethyl-2,6-di / tert-butylperoxy / hexane] and 18 parts of low density polyethylene were used.

The temperatures in the four control zones were 215, 270, 225, 180 ° C and the extruder head temperature was 200 ° C. The screw speed was 130 rpm.

The resulting polymer blend had a flow index = 37 g / 10 min.

The polymer blend was extruded from a slit die to a paper speed of 60-220 m / min. The polymer blend was 15 to 40 g / m < 2 > and was uniform in the longitudinal and transverse directions. The narrowing of the melt curtain was 1.2 cm at each edge, while for polypropylene with a flow index = 40 g / 10 min, it was 8 cm at each edge under the same conditions.

Example 3

The procedure was analogous to Example 1, with the following differences. The stabilization system was formed of 0.15 parts of phenolic stabilizer [pentaerythritol-tetra-beta / 4-hydroxy-3,5-di-tert-butylphenol / propionate], 0.1 parts of phosphite stabilizer [tris- (1 * phenyl-4-ethylphenyl)] phosphorous acid ester] and 0.07 parts of a secondary sulfur antioxidant (distearyl thiodipropionate).

The peroxide initiator (dicumyl peroxide) was added in an amount of 0.07 parts. The mixture was mixed in a fluidic mixer at 25 ° C for 45 minutes. Then 10 parts of low density polyethylene powder with a flow index ⁼ 7 g / 10 min and 10 parts of low density polyethylene powder with a flow index = 70 g / 10 min were added. The mixture was stirred for 30 minutes at the same temperature. By extrusion under the conditions of Example 2, a polymer mixture having a flow index of 49 g / 10 min was obtained.

The polymer blend was extruded from a slit paper die at a speed of 60 to 220 m per minute. The polymer blend was 15 to 40 g / m < 2 > and was uniform in the longitudinal and transverse directions. The narrowing of the melt curtain was 1.1 cm at each edge, while for polypropylene with a flow index = 40 g / 10 min. was 8 cm at each edge.

Example 4

The procedure was analogous to Example 3, with the following differences.

The peroxide initiator (dicumyl peroxide) was used in an amount of 0.12 parts. The polypropylene with stabilizers and initiator was fed in parallel with the low density polyethylene granulate with a flow index = 20 g / 10 min.dc of the extruder operating under the conditions of Example 1.

The resulting polymer blend contained 12 parts of low density polyethylene and had a flow index of 32 g / 10 min. The polymer blend was extruded from a slotted paper die at a speed of 60 to 220 m / min. The deposition of the polymer blend was 15 to 40 g / m < 2 > and is uniform in the longitudinal 1 transverse direction. The narrowing of the melt curtain was 2.1 cm at each edge, while for polypropylene having a flow index = 40 g extruded for 10 minutes under the same conditions it was 8 cm at each edge.

Claims (1)

SUBJECT OF THE INVENTION Process for preparing blends of polypropylene and low density polyethylene for extrusion coating, comprising 80 to 95% by weight of polypropylene having a flow index reduced by radical degradation and 5 to 20% by weight of low density polyethylene having a flow index of 2 to 70 g / 10 min at 270 ° C and 23 N stabilizers and processing additives by extrusion, characterized in that the blend of powdered polypropylene having a flow index of 0.2 to 10 g / 10 min. at 190 ° C and 21.2 N and low density polyethylene is melted and kneaded at a temperature of 150 to 300 ° C in the presence of 0.02 to 0.2 parts by weight of organic peroxides and 0.1 to 0.6 parts by weight of a synergistic mixture of phenolic stabilizers, phosphites and sulfur antioxidants per hundred parts of the polyolefin mixture.