CS217079B1 - Stabilizing concentrate for low pressure polyethylene - Google Patents

Abstract

The invention relates to stabilizer concentrates for low-pressure polyethylene containing polyethylene ε 2 to 20% by weight of stabilizing additives. The polyethylene in the stabilizer concentrate is low-pressure polyethylene with a flow index of 2 to 17 g/min, which contains 1 to 2.5 weight fractions with a molecular weight of up to 10^ and 0.5 weight % of a fraction with a molecular weight of more than 10

Description

The invention relates to stabilizing concentrates for low pressure polyethylene.

Low and high density polyethylene wipes that are exposed to solar radiation have a significantly reduced lifetime. They gradually lose their good mechanical properties and become brittle. This undesirable effect is all the more apparent the thinner the finished products.

In part, the service life of polyethylene products can be prolonged by the fact that the basic polymer mixture is stabilized by antioxidants, in particular of the phenolic type, which prevent oxidative degradation both when the starting polymer is processed and when the finished products are applied.

In order to achieve greater stability against the effects of solar radiation, substances which are capable of absorbing ultraviolet solar radiation and bringing them to inactive radiation of greater wavelengths are added to the polymer blend. Typical representatives of this class of compounds are derivatives of selicylic acid, benzotriezole, optionally benzophenone. In some cases, substances that are capable of extinguishing excited states of certain functional groups on the polymer chain and thereby protecting the polymer against photooxidative degradation are added to the polymers. Such compounds are, for example, some complex nickel compounds and a number of piperidine and piperazine derivatives.

A very serious problem is the homogeneity of dispersion of these substances in the polymeric material.

In connection with this problem, there are two basic ways of dispensing these substances into polymers. A powder mixture of the respective polymer with stabilizers is prepared, whether continuously or discontinuously, which is homogenized in a further extruder and granulated. Another method of stabilization is to use a granular stabilizing concentrate which is mixed by the processor into the granular or powdered unstabilized polymer in a ratio such that the desired stabilizer concentration is achieved in the final product.

Up to now, low molecular weight, high pressure, high flow index polyethylenes which have a good dispersion due to their low softening point have been used in other polyolefin polymers to produce these concentrates. These concentrates must be metered into the polymers in a quantity of a few percent, so their concentration is not negligible and can therefore significantly affect the mechanical properties of the final product. Since the concentrates also need to be applied in high-density polyethylenes produced by a fluidized bed polymerization, other carriers have been sought to balance all the basic good properties required for dispersion, i.e. the possibility of preparing a homogeneous mixture of stabilizers and base carrier, good carrier compatibility. with unstabilized linear polyethylenes, little effect of polymeric carrier on the basic mechanical properties of the final product.

The stabilizing concentrate for the low pressure polyethylene of the present invention meets these requirements.

SUMMARY OF THE INVENTION The present invention provides a stabilizing copolymer for low pressure polyethylene containing 60 to 98% by weight polyethylene and 2 to 20% by weight stabilizing additives such as benztriazoles, benzophenones, sulfides, piperidine derivatives, fenply, phosphites and thiedipropionic acid esters, wherein polyethylene in the stabilizing concentrate is a low pressure polyethylene having a flow index of 2 to 17 g / min and containing 1 to 2.5% by weight of a molecular weight fraction up to. And up to 0.5% by weight of a fraction with a molecular weight greater than 10.

In experiments with various types of low-pressure polyethylenes used as carriers, it has been found that the carrier polymer has to exhibit quite specific properties which allow for perfect dispersion in the next phase of use of the concentrate. If the carrier polymer has more than 0.5% by weight of the high molecular weight fractions having a molecular weight of MW = 10 ° and above, melt is poorly homogenized in the preparation of concentrates if the carrier polymer contains>>

More than 2.5% by weight of low molecular weight fractions of KW. If the concentrate is well homogenized, the low molecular weight fractions adversely affect the final mechanical properties of the product stabilized by the concentrate. However, if the carrier polymer used is less than 1% by weight of the low molecular weight fractions, the stabilizer additives are poorly dispersed.

The prior art methods for the preparation of concentrates are based on homogenization of non-specific polymer mixtures based on high pressure polyethylenes using dispersants. However, their use introduces a new component into the product, affecting their thermooxide and photooxidation stability.

In addition to this adverse effect, the final product does not complicate the production of semiconductive concentrate, which is reflected in the price of these products.

Optimum homogenization of the carrier polymer with the stabilizing additives is made possible by the appropriate choice of the polymer, optionally through deliberate polymerization. The low molecular weight fractions of the prescribed molecular weights and concentrations already serve as the ultimate dispersant in the preparation of the concentrates, thereby rendering the concentrate preparation process highly efficient.

The following examples illustrate the invention. % by weight are by weight unless otherwise stated.

Powdered high-density polyethylenes produced by fluidized bed polymerization were used as polymer carriers in the examples:

Type A having a flow index of 0.05 to 0.12 g / min, which was defined by gel permeation chromatography (GPC) with the following parameters: Average molecular weight MZ = 92,000, the weight average molecular weight and iJ = 191,000, the number average molecular weight mass MN = 5,000.

Type B with a flow index of 3.2 to 4.7 g / 10 min. defined by GPC with the following parameters: average molecular weight MZ = 1,448,000, weight average molecular weight MW = 248,000, number average molecular weight MN = 31,000. Type G with a flow index of 0.1 to 0.18 g / 10 min. defined by GPC with the following parameters: Average molecular weight MZ = 1,133,000, average molecular weight MV / = 178,000, number average molecular weight MN = 16,000.

Type D with a flow index of 5 to 7 g / 10 min. defined by GPC with the following parameters: Average molecular weight MZ = 288,000, weight average molecular weight MV / = 73,000, number average molecular weight MN = 13,000. Furthermore, it has been found that powder type D does not contain in a detectable amount a fraction higher than MW = 10 µm. The MW fraction below 10% is below 2%.

Type E with a flow index of 13 to 17 g / 10min. defined by GPC with the following parameters: Average molecular weight MZ = 223.OOO, weight average molecular weight MW = 44.OOO, number average molecular weight MN = 7.000, fraction greater than MW = 10 ^ was 0.3%, fraction content with MV / less than 10 ^ is 1.8 ¢.

Example 1

In the mixer behind. Herfeld was homogenized in powder form with a mixture containing 86.0% low pressure polyethylene type D, 10% 2- (2-hydroxy-3 (tert-butyl-5'-methylphenyl) 5-chlorobenzotriazole (I) and 4% tetrakis-methylene-3- (3). 5 ', - (di-tert-butyl-4-hydroxy-phenyl-propionate) methane (II) The polymer blend was extruded on a Centrotechnica extruder and granulated. A melt containing 0.3% I and 0.12% II was obtained by compression, and a 0.5 mm thick film was exposed by Xenotest and the photooxidation progress was monitored by measuring the concentration of carboxyl groups by infrared spectroscopy. = 1580 h) represents the efficiency of the stabilization system used.

Example 2

Polyethylene powder type C was homogenized in a Brabender plastograph and 0.3% I and 0.12% II. A sheet of 0.5 mm thickness was prepared by compression and, as in Example 1, the photooxidation stability was observed. The induction period of 1560 h indicates perfect homogeneity of the material shown in Example 2.

Example 3

In a Uerfeld mixer, a blend containing 86.0 '% low-pressure polyethylene type A, 10% 2- (2'-hydroxy-3'-tert-butyl-5'-methyl-phenyl) 5-chlorobenzotriazole I and 4% tetrakis - (methylene-3- (3'-5'-di-tert-butyl-4-hydroxyphenyl propionate) methane II) The polymer / additive mixture was extruded on a Uentrotechnica extruder and granulated. after 10 minutes of kneading in a Brabender kneader, a melt containing 0.3% I and 0.12% II was obtained, and a 0.5 mm thick film was exposed by compression and exposed to Xenotest, and photooxidation was monitored by infrared spectroscopy. The period (960 h) represented the efficacy of the stabilizing system used, and microscopic examination showed that there was no homogeneous dispersion of the UV absorber.

Example 4

As described in Examples 1 and 3, a concentrate was prepared using polyethylene of type *

The concentrate was mixed in an amount of 3% with powdered polyethylene and after 10 min. kneading obtained a melt containing 0.3% I and 0.12% II. A foil with a thickness of 0.5 mm was prepared by pressing and was exposed in Xenotest. The induction period was 830 min. Microscopic examination revealed no homogeneous dispersion of the UV absorber.

Example 5

As described in Examples 1, 3 and 4, a concentrate was prepared using polyethylene type C and appropriate stabilizing ingredients. The concentrate was mixed at 3% 8 with polyethylene powder type C and after 10 min. kneading obtained a melt containing 0.3% I and 0.12% II. A foil with a thickness of 0.5 mm was prepared by pressing and exposed in a Xenotest. The photooxidation induction period was 890 min. Microscopic examination revealed that it did not homogeneously disperse the UV absorber.

Example 6.

In a Herfeld mixer, a blend containing 90% low pressure polyethylene type D, 5% piperidine polymer stabilizer III and 5% tetrakis (methylene-3 '- 5-di-tert-butyl-4-hydroxyphenyl propionate) methane II antioxidant was homogenized in powder form. The polymer / additive mixture was extruded through an Oentrotechnica extruder and granulated.

The obtained concentrate was mixed in an amount of 2% with powdered polyethylene C and after 10 min. kneading in a Brabender kneader obtained a melt containing 0.1% III and 0.1% II. A sheet of 0.5 mm thickness was prepared by compression and exposed to < Xenotest. The length of the induction period of 4100 h confirms the perfect homogeneity of the stabilizer distribution.

Example 7

Polyethylene powder type C was homogenized in a Brabender plastograph with 0.1% III and 0.1%. A sheet of 0.5 mm thickness was prepared by compression, and the photooxidation stability was monitored as in Example 6. The length of the photooxidation induction period was 4050 h.

Example 8

As described in Example 1, a concentrate of 89.5% high density polyethylene type D, 10% I with 0-5% di-tert-butyl p-cresol IV antioxidant was prepared. The concentrate was mixed with 3% polyethylene powder of type C as described in Example 1 and evaluated for photooxidation stability of the final blend by Xenotest. The length of the induction period of 1560 is indicative of the system's efficiency.

Example 9

As described in Example 1, a concentrate was prepared using low pressure polyethylene type D granules. The stabilizing efficiency of the concentrate obtained was equivalent to that obtained from a powdered polymer having a flow index of 6.

Example 10

As described in Example 1, a concentrate was prepared using 50% powdered and 50 granulated polyethylene type D and appropriate stabilizers. The stabilizing efficiency of the obtained concentrate was equivalent to those obtained from a powdered polymer having a flow index of 6.

Example 11

As described in Example 1, a concentrate was prepared using low pressure polyethylene, type E, with a flow rate of 15 g / min. The stabilizing efficiency of the concentrate obtained was equivalent to the values obtained using a concentrate prepared with a polymer having a flow index of 6 g / min. Example 12

Concentrates containing 86.0% low pressure polyethylene type D were prepared as described in Example 1. 10% I and 4% antioxidant of either tris nonylphenyl phosphite or disteerylthiopropionate or dioctadecyldisulphide or mixtures thereof with II. The stabilizing efficiency of the concentrate obtained was equivalent to that obtained in Example 1.

Claims (1)

SUBJECT OF THE INVENTION Stabilizing concentrate for low-pressure polyethylene containing 80 to 98% by weight polyethylene and 2 to 20% by weight stabilizing additives such as benzotriazole, benzophenones, sulfides, piperidine derivatives, phenols, phosphites, thiodipropionic acid esters, characterized in that the polyethylene in the stabilizing concentrate is low pressure polyethylene having a flow index of 2 to 17 g / min containing 1 to 2.5 weight percent fractions having a molecular weight of 10 µm and 0.5 weight percent fraction with a molecular weight of greater than 10 µm.