RU2756586C1 - Thermoplastic composition - Google Patents

Abstract

FIELD: composite materials.

SUBSTANCE: invention relates to a thermoplastic composition intended for use in the cable industry, in the production of packaging material and other products. The composition contains the following components, by wt.%: 91.5-91.9 low-density polyethylene, 0.1-0.2 phenolic or phosphite type heat stabilizer, 8.0-8.3 UV light stabilizer. An ester of 3,5-di-tert-butyl-4-hydroxyphenylpropionic acid and pentaerythritol is used as a phenolic type heat stabilizer, a mixture of 3,5-di-tert-butyl-4-hydroxyphenylpropionic acid ether and pentaerythritol and tri-(2,4-di-tert-butylphenyl)phosphite in a mass ratio of 1:1 is used as a phosphite type heat stabilizer, the UV light stabilizer uses a 30% carbon black concentrate based on low-density polyethylene.

EFFECT: invention makes it possible to increase the technological parameters of the composition, in particular, to increase the fluidity of the melt, thermal stability and resistance to cracking, while maintaining the operational properties of the products obtained from it at a high level.

1 cl, 2 tbl, 12 ex

Description

The invention relates to the chemical industry, in particular, to the composition of thermoplastic compositions based on low density polyethylene and can be used in the cable industry, in the production of packaging material and other products.

Low density polyethylene (LDPE) is a versatile polymer that can be used in a variety of applications such as films, coatings, molded products, and wire and cable insulation. Polyethylene is used on a large scale to make pipes, which require a material with high mechanical strength and high resistance to stress cracking due to environmental factors, in addition, the material must be able to be easily processed in the manufacture of pipes.

Currently, polymer compositions intended for use in the cable industry are produced in accordance with GOST 16336-2013 "Composition of polyethylene for the cable industry". One of the most important characteristics of compositions intended for obtaining an insulating sheath of an electric cable is resistance to stress cracking, which, in accordance with GOST 16336-2013, should be at least 500 or 1000 hours, depending on the grade of polyethylene.

It is known that cracking resistance is a complex characteristic and depends on several factors, in particular on the thermal stability of the polymer. Therefore, one of the possible directions for increasing the resistance to cracking is the use of heat stabilizers in the composition of polymer compositions. An efficiently selected thermal stabilizer protects the polymer from thermal oxidative degradation, which can contribute to an increase in resistance to cracking. Another way to increase the resistance to cracking of the compositions is the introduction of modifying additives into the composition of the polymer composition. However, a review of the literature data showed that currently there are no effective modifiers that significantly increase the resistance to cracking without deteriorating other characteristics of the polymer.

Another important indicator characterizing the quality of the plasticized composition is the melt flow rate (MFR). The MFI is a parameter that determines the manufacturability of the polymer and the method of its processing. The higher the MFI of the composition, the lower its viscosity and the higher the processing rate - the better the manufacturability. It is the low MFI that makes it difficult to process the polymer and requires high extrusion temperatures.

The most popular polymer compositions intended for use in the cable industry are compositions of grades 153-02K and 153-10K based on LDPE grade 15313-003 obtained in a tubular reactor. For these compositions, the index of resistance to cracking in accordance with the standard GOST 16336-2013 is at least 1000 hours, but the MFI values are at a low level and range from 0.21 to 0.39 g / 10 min.

Known polymer composition based on LDPE with the addition of talc, zinc oxide, calcium stearate (RF patent No. 368279, publ. 01/26/1973). The resistance to cracking of this composition does not exceed 285 hours.

The composition, declared in the patent WO No. 0248258 (publ. 20.06.2002), intended for extrusion coating and films, consists of three components: linear low density polyethylene, high density polyethylene, LDPE. The resistance to cracking of this composition is 312 hours.

The main disadvantage of the compositions indicated in these patents is their low resistance to cracking, which limits the range of application of these compositions.

CN patent No. 106220940 (publ. 12/14/2016) proposes a composition with high resistance to stress cracking, which includes LDPE, terpene resin, methylphenylsilicone resin, acetyltributyl citrate, binding agent TMS-201, triphenyl phosphate, antioxidants, oils , cellulose. Such compositions can be used for the manufacture of a building optical cable sheath and have sufficiently high strength characteristics. However, the use of a large number of components of a complex composition leads to an increase in the cost of products obtained on its basis.

A known composition containing LDPE, linear polyethylene, high density polyethylene, as well as nucleating agents that regulate the crystallization rate of macromolecules (application WO No. 2019132694, publ. 04.07.2019). Inorganic compounds (preferably carbon black, talc) and organic compounds (preferably 3,4-dimethyldibenzylidene sorbitol, zinc stearate and calcium salt of 1,2-cyclohexanedicarboxylic acid) can be used as nucleating agents. The composition may contain other additives such as antioxidants, heat stabilizers, light stabilizers, or mixtures thereof. This composition has high strength and elastic characteristics, high resistance to stress cracking (not less than 2000 hours), the MFI of the composition is in the range from 0.24 to 1.10 g / 10 min and can be used both for the production of high-quality films and for insulating coatings for electrical cables. The disadvantage of this composition is the multicomponent composition of the composition, which includes different types of polymers, due to which it may be difficult to select the temperature regimes for processing the composition and the risk of insufficient uniformity of the distribution of components in it. For cable covering, the occurrence of heterogeneity, the formation of agglomerations leads to a deterioration in the insulating properties. In addition, the selection of the optimal components of the composition and their amount for the use of the composition in a certain area is a rather difficult task and leads to an increase in the cost of the product.

A known method of obtaining a highly filled polyolefin composition with modifying additives (RF patent No. 2721913, publ. 05/25/2020), in which a pre-prepared modifying additive is introduced into the polymer matrix in an amount of 3 wt.%, Then a filler calcium carbonate in an amount of 50- 60 wt%. High pressure polyethylene is used as a polymer matrix, the modifying additive is a concentrate containing calcium stearate and stearic acid, taken in a weight ratio of 2: 1, with a total content of 20 wt%. The disadvantage of this method is the low strength characteristics of the resulting composition.

The closest in technical essence (prototype) is the invention under the patent of the Russian Federation No. 1746693 "Polymer composition", including high-pressure polyethylene and organic phosphorus- and sulfur-containing stabilizer - tri- (3,5-di-tert-butyl-4-hydroxyphenylmercapto) phosphite. The additive is introduced into the base polymer in an amount of 0.1-0.5 wt%. However, this patent does not describe the effect of the stabilizer used on other physical and mechanical properties of the polymer composition, except for thermal stability.

The aim and technical result of the claimed technical solution is to obtain a thermoplastic composition based on LDPE with a minimum content of additives, with improved technological parameters, in particular, increased melt flow, thermal stability and resistance to cracking, while maintaining a high level of operational properties of products obtained from it.

The specified technical result is achieved by the development of a thermoplastic composition including low density polyethylene and stabilizers, while a phenolic type or phosphite type heat stabilizer and a UV light stabilizer are used as stabilizers, while 3,5-di-tert-butyl ether is used as a phenolic type heat stabilizer. -4-hydroxyphenylpropionic acid and pentaerythritol, a mixture of 3,5-di-tert-butyl-4-hydroxyphenylpropionic acid ester and pentaerythritol and tri- (2,4-di-tert-butylphenyl) phosphite is used as a phosphite-type thermal stabilizer, as The UV light stabilizer uses a 30% carbon black concentrate based on low density polyethylene, with the following ratio of components, wt%:

Low density polyethylene 91.5 - 91.9

Heat stabilizer of phenolic or phosphite type 0.1 - 0.2

UV light stabilizer 8.0 - 8.3

LDPE manufactured at Kazanorgsintez PJSC with the following main characteristics was chosen as the basis for obtaining the composition: tensile yield strength is 12.0 MPa, tensile strength - 16.2 MPa, elongation at break - 610%, MFI - 0.76 g / 10 min, mass fraction of extracted substances - 0.5%, resistance to cracking - 12 hours.

In the present invention, compounds of the phenolic type, for example, Irganox 1010, or of the phosphite type, for example, Irganox B225, are used as heat stabilizers. Irganox 1010 is a primary antioxidant, belongs to the class of sterically hindered phenols. Irganox B225 is a synergistic mixture of primary and secondary antioxidants Irgafos 168 and Irganox 1010, taken in a 1: 1 weight ratio. Stabilization of polyethylene with mixed stabilizers of the Irganox B225 type provides an additional improvement in the properties of materials by preventing thermo-oxidative and thermal destruction of the molecules of the components that make up the material.

To obtain compositions that are resistant to photooxidative degradation, a UV light stabilizer, carbon black, is used, which is preferably introduced through a 30% industrial concentrate based on LDPE. Carbon black is an effective light stabilizer for polymer compositions that are prone to structuring when exposed to UV rays, which leads to a decrease in such indicators as tensile strength and elongation at break.

The properties of the polymer composition were evaluated by the change in the physical and mechanical characteristics of the plates and films using standard techniques:

- MFI was determined at a temperature of 190 ° C and a load of 2.16 kgf in accordance with GOST 11645;

- tensile yield strength, breaking strength and elongation at break were determined in accordance with GOST 11262 at a test speed of 500 mm / min;

- resistance to cracking was determined in accordance with GOST 135183;

- thermal stability at a temperature of 200 ° C was determined by the method of differential scanning calorimetry in accordance with GOST 50838;

- the strength of the films in the longitudinal and transverse directions, as well as the relative elongation at break in the longitudinal and transverse directions were determined in accordance with GOST 14236-81 using a testing machine;

- the content of gels was determined in accordance with GOST 16337-77.

To illustrate the technical result achieved during the implementation of the proposed invention, examples are given with the most indicative ratios of the components of the composition. The invention is illustrated by the following examples.

Example 1 (prototype).

99.9 wt% LDPE is mixed with 0.1 wt% phosphite S in a paddle mixer until the components are uniformly mixed. The resulting mixture is fed to a twin-screw extruder for melting and homogenizing. The melt temperature at the exit from the extruder die is 170 ° C. The strands obtained are cooled in a water bath and cut into granules of 3-5 mm in size.

Example 2 (proposed method).

91.6 wt.% LDPE is mixed with 0.1 wt.% Irganox 1010 and with 8.3 wt.% 30% carbon black concentrate in a mixer with a paddle stirrer until the components are uniformly mixed. The resulting mixture is fed to a twin-screw extruder for melting and homogenizing. The temperature of the melt at the exit from the extruder die is 175 ° C. The strands obtained are cooled in a water bath and cut into granules of 3-5 mm in size.

Example 3-12

The preparation of the composition is carried out under the conditions of example 2, but the components are used in a different ratio. The compositions of the compositions according to the examples are shown in table 1.

Table 1. Compositions of thermoplastic compositions Example No. LDPE, wt% Carbon black concentrate, wt% Thermal stabilizer, wt% Irganox 1010 Irganox B225 phosphite S 1 99.9 - - - 0.1 2 91.6 8.3 0.1 - - 3 99.9 - 0.1 - 4 99.8 - 0.2 - 5 99.9 - - 0.1 - 6 99.8 - - 0.2 - 7 91.5 8.3 0.2 - - eight 91.6 8.3 - 0.1 - nine 91.5 8.3 - 0.2 - ten 91.5 8.3 0.1 0.1 - eleven 91.8 8.0 0.1 0.1 - 12 100.0 - - - -

To carry out physical and mechanical tests, samples are made from the obtained granules: for all compositions, plates with a thickness of 2-3 mm are made by hot pressing; For compositions without the addition of a UV light stabilizer, a film with a width of 90-100 mm and a thickness of 0.04-0.05 mm is made by extrusion blowing at a temperature of 160-185 ° C. The results of physical and mechanical tests of the obtained samples and films are shown in Table 2.

The test results show that the claimed compositions according to examples 2-11 with the introduction of heat stabilizers and UV light stabilizer have, in comparison with the prototype, higher resistance to cracking and thermal stability, better physical and mechanical properties. The claimed compositions are characterized by an optimal MFI level to improve processing.

Compositions according to examples 3-6 with the use of a heat stabilizer, but without the use of a UV light stabilizer, along with a high level of physical and mechanical properties and thermal stability, are characterized by high film properties. The combination of such properties allows the compositions to be used both for obtaining strong and elastic films and for cable insulation, without the need for UV stabilization.

Compositions according to examples 2, 7-11 using heat stabilizers and UV light stabilizer demonstrate the most optimal properties for use as an outer insulating sheath of an electric cable. Along with a high MFI, which improves polymer processing, the compositions have a higher thermal stability, which indicates that the UV light stabilizer enhances the thermal stabilizer effect. In addition, these compositions have a high level of resistance to cracking, which is one of the most important indicators for the cable industry.

Thus, the proposed composition has improved physical and mechanical properties, which makes it possible to increase the manufacturability of processing the polymer composition, as well as to improve the performance properties of products obtained from it.

Table 2. Physical and mechanical properties of prototypes and films Name
indicators Parameters by example Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 Example 9 Example 10 Example 11 Example 12 Indicators for plates MFR, g / 10 min 1.8 0.68 0.78 0.77 0.76 0.74 0.69 0.70 0.68 0.71 0.71 0.76 Tensile yield strength, MPa 9.4 11.6 10.8 10.6 10.9 11.3 11.2 11.4 11.5 11.0 11.0 12.0 Breaking strength, MPa 12.5 14.2 13.1 13.0 13.4 13.6 14.0 14.0 14.0 14.1 14.1 16.2 Elongation at break,% 540 600 560 560 580 590 600 600 600 600 600 610 Cracking resistance, h 24 more than 1100 more than 1100 more than 1100 more than 1100 more than 1100 more than 1100 more than 1100 more than 1100 more than 1100 more than 1100 12 Thermal stability at 200 ° C, by differential scanning calorimetry, min 31 82 39 42 45 59 80 78 70 72 72 0 Indicators for films Tensile strength, MPa
- in the longitudinal direction
- in the transverse direction 14.2
13.3 -
- 22.3
18.5 21.7
18.6 22.0
19.1 21.9
19.4 -
- -
- -
- -
- -
- 21.5
19.7 Elongation at break,%
- in the longitudinal direction
- in the transverse direction 280
300 -
- 360
350 360
350 350
350 360
350 -
- -
- -
- -
- -
- 330
360 Number of gels ranging in size from 0.5 to 1.0 mm inclusive, pcs fourteen - 7 ten nine eight - - - - - nine

Claims (2)

A thermoplastic composition for products, including low density polyethylene and stabilizers, characterized in that a phenolic type or phosphite type heat stabilizer and a UV light stabilizer are used as stabilizers, while 3,5-di-tert-butyl ether is used as a phenolic type heat stabilizer. 4-hydroxyphenylpropionic acid and pentaerythritol, a mixture of 3,5-di-tert-butyl-4-hydroxyphenylpropionic acid ester and pentaerythritol and tri- (2,4-di-tert-butylphenyl) phosphite in a mass ratio of 1 : 1, a 30% carbon black concentrate based on low density polyethylene is used as a UV light stabilizer, with the following ratio of components, wt%: Low density polyethylene 91.5-91.9 Heat stabilizer of phenolic or phosphite type 0.1-0.2 UV light stabilizer 8.0-8.3