CS252989B1 - Thermoplastic elastomer composite of rubber and polyethylene - Google Patents

Abstract

The thermoplastic elastomer composite is particularly suitable for the cable industry. The aim of the solution is to obtain elastomeric materials with processing properties of thermoplastics, which can be vulcanized by a vulcanization system. The composition consists of an elastomeric and a thermoplastic component, wherein the elastomeric component comprises 8.0 to 90% by weight of styrene-diene rubber with a maximum of 45% by weight of styrene, based on an ethylene-propylene-diene terpolymer having a content of 40 to. 90% by weight of ethylene, preferably of the sequential type and / or mixtures thereof with natural rubber and the thermoplastic component comprise 0.3 to 31% by weight of polyethylene with a melt index of 180 to 220 and / or 0.1 to 58% by weight of polyethylene with a melt index of 0 1 to 20 and the composition preferably comprises a filler in the range of 0.0 to 800 parts by weight per 100 parts by weight of rubber. A sulfur-free and accelerator-free composition with a high level of filling is suitable as a filler material for use in the electrical industry.

Description

The invention relates to thermoplastic elastomer compositions, suitable in particular for ^cable purposes, comprising copolymers of rubber or a mixture of rubbers and polyethylene with a high melt index, vulcanizable with sulfur or a sulfur vulcanization system.

The purpose of the solution is to obtain an elastomeric material with thermoplastic properties, which will improve the processing of rubber mixtures, as well as improve the technological properties of the product. When using sulfur, thermoplastic elastomers prepared by dynamic vulcanization are obtained at elevated temperatures, which can be used in the cable industry, especially as insulating and sheathing materials for cables and cable fittings. Without the use of vulcanizing additives and with an increased content of fillers, materials suitable for filling mixtures between cable cores are obtained. The mixtures prepared in this way have excellent rheological properties and, in comparison with other mixtures used, improved technical properties. They also mean economic benefits in terms of production volume indicators, labor productivity and energy savings.

Thermoplastic elastomers are known as two-phase materials that can be processed as plastics at temperatures higher than the melting point of the plastomeric phase, but have the physical properties of elastomers at lower ^temperatures . They can be used to produce products by extrusion, injection molding or molding as plastics, omitting the vulcanization process, while the waste from production can be recycled several times without any regeneration and without significant impact on the properties of the material.

Many thermoplastic elastomers based on a mixture of rubber and plastic are known from the patent literature. Most of them are focused on a mixture of monoolefinic copolymer or terpolymer rubber EPM and EPDM with polyolefins. Such mixtures have excellent mechanical, elastic and electrical properties, but without the addition of crosslinkers they show low thermal stability. The above-mentioned deficiency can be largely eliminated by partial or complete crosslinking of the rubber component by the method of dynamic vulcanization in the process of mixing the mixture in a high-speed mixing device heated to a temperature of 180 ° C, as described, for example, in patents US 3 758 643, US 3 862 106, CS 198 202 or FR 2 323 734.

Thermoplastic elastomers prepared on the basis of a combination of EPDM and polyethylene or polypropylene usually contain 40 to 60 parts by weight of polyolefin per 100 parts of rubber. The stated amount of polyolefin is necessary to create a continuous plastomeric phase, ensuring the thermoplasticity of the material. When dosing polyolefin below 30 parts by weight, a thermoset is obtained, which loses its advantageous thermoplastic properties. When the concentration of polyolefin exceeds 80 parts by weight per 100 parts of rubber, a hard material with low elastic properties is obtained. The crosslinked elastomer component dispersed in the continuous plastomeric phase largely influences the toughness of the mixture, which ensures greater resistance to tearing and abrasion of the material. The toughness of the mixture can be characterized by the expression (TSj ² /E, where TS is the tensile strength and E is Young's modulus of elasticity. To improve the processing properties of rubber mixtures, especially at higher filler contents, various plasticizers are used. The most common are various oils, resins, factice and asphalt in thermoplastic elastomers, for example according to patents CS 198 202, NDR 126 193, CS 201796. However, these plasticizers all deteriorate the electrical properties of the material, plasticizers migrate, which negatively affects not only the physical properties of the material at elevated temperatures, but also the aging process of the material itself, they discolor the mixtures and limited compatibility with rubbers leads to processing problems at higher plasticizer contents, such as increased stickiness to equipment and the formation of gas cavities in the product.

Various types of polyethylene are used to improve the physical properties of thermoplastic elastomers. In patent CS 196 337, polyethylene with a melt index of 0.6 is used, which is unsuitable for extrusion and injection molding. In patent CS 205 674, polyethylene with a melt index of 20 to 200 is used, but in a dosage of 1 to

9.5 weight percent. However, the stated dosage does not allow sufficient material processability due to the low concentration of the plastomeric component. Increasing the content of the stated polyethylene itself causes stickiness to technological equipment. Modification of the properties of rubber mixtures when using polyethylene with a high melt index is solved by some authors using crosslinking with peroxide or radiation, which results in an irreversibly crosslinked vulcanizate - a copolymer of rubber and polyethylene. After vulcanization, polyethylene loses its original function of a high-molecular plasticizer, such as in mixtures based on EPDM rubber in patent CS 175 785.

Improving the processability of thermoplastic materials by increasing the dosage of the base polyolefin is not suitable because the toughness and elastic properties of the mixture decrease significantly with increasing the content of low melt index polyethylene.

The above-mentioned shortcomings are solved by the invention, the essence of which is the modification of rubber mixtures with polyethylene with a high melt index in the range of 180 to 220 in combination with polyethylene with a melt index from 0.1 to 20.

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The thermoplastic elastomer composite consists of 23 to 90 weight percent of styrene-butadiene rubber with a content of max. 45 weight percent of styrene or its mixture with ethylene propylene copolymer or thermoplastic polymer with a polyethylene content of 40 to 90 weight percent, preferably of the sequential type, or their mixture with natural rubber, to which is added 0.3 to 31 weight percent of polyethylene with a melt index of 180 to 220 and a proportion of polyethylene with a melt index of 0.1 to 20 in an amount of 0.1 to 58 weight percent. Other components of the composition are 0.1 to 21 weight percent of a plasticizer; The method of application of the mixture according to the invention may further comprise a sulfur vulcanization system in an amount of 0.0 to 2.5 weight percent of sulfur and 0.0 to 3 weight percent of a thiuram-type accelerator and preferably also an inorganic filler or carbon black in an amount of 0.0 to 800 weight parts per 100 weight parts of the rubber mixture. To increase the resistance of the mixture to the effects of ozone and oxidation, it is possible to add stabilizing additives.

The thermoplastic elastomer mixture is prepared on a conventional mixing device at a temperature of 160 to 170 °C and a speed of 3.0 to 100 rpm. Rubber, PE, filler, stearin and finally vulcanization additives were gradually added so that these components reacted. Under these conditions, the preparation cycle lasted 10 to 15 minutes with an active time of the vulcanization system of 3 to 10 minutes, which achieved practically complete crosslinking of the rubber without further physicochemical changes of the mixture during their further processing during application. After mixing all components, the mixtures were briefly homogenized on a double roller.

Table 1 contains examples of blend compositions and their mechanical properties, where only the content of high melt index polyethylene was changed — increased.

Table 1

Components (mass d. j example no. 1 2 3 4 5 SBR rubber 65 65 65 65 65 EPDM rubber 35 35 35 35 35 polyethylene with melt index 2.0 50 50 50 50 50 soot 25 25 25 25 25 stearin 1.0 1.0 1.0 1.0 1.0 sulfur 0.4 0.4 0.4 0.4 0.4 TMTD accelerator 0.8 0.8 0.8 0.8 0.8 polyethylene with melt index 200 0 5 10 20 30 100% modulus MPa 2.62 2.60 2.86 3.08 2.82 tensile strength MPa 5.75 5.75 5.75 5.96 4.05 elongation at break % 670 640 640 650 520 Shore A hardness 75 75 74 74 72 in _crit . s ¹ , 190 °C 3.5 98 204 771 4,320 TS ² /E MPa 7.13 7.13 6.21 6.23 3.02 viscosity at 190 °C MPa . s 17.6 15.0 5.8 2.25 0.86 torque N . m 24.26 26.25 25.32 23.33 21.35

The addition of PE with a high melt index significantly affects the properties of thermoplastic elastomers, especially the value of the critical shear rate — V _k(it , measured on an extrusion viscometer at 190 °C, with a nozzle L = 15 D with a flat inlet area, which characterizes the processability of materials by extrusion and injection molding. A slight deterioration in the mechanical properties and toughness of the material is not a defect with appropriate PE dosage. A significant reduction in the viscosity of the mixture and a decrease in the torque Mkrut. in practice means a reduction in energy consumption requirements.

Omitting the thiuram accelerator from the composition of the mixture may not cause a significant deterioration in the technical properties of the mixture and ensures better homogenization of the crosslinker — sulfur until the beginning of dynamic vulcanization. Examples of mixtures crosslinked with sulfur without the presence of the thiuram accelerator of vulcanization with various types of filler are given in Table 2.

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Table 2

Components (wt. d.) example no. 6 7 8 9 10 SBR rubber 100 67 67 67 67 EPDM rubber II, ML (1 + 4)/100°C; 85 — 33 — 33 17.5 EPDM rubber II, ML (1 + 4)/100 °C; 85 — — 33 — 17.5 polyethylene with melt index 2.0 70 50 50 50 60 polyethylene with melt index 200 5 15 15 5 5 soot — 30 30 — 30 precipitated silicon dioxide — — — 30 — annealed kaolin 20 — — — — paraffin 1.0 — — — 3.5 sulfur 3.0 0.5 0.5 0.5 0.5 100% modulus MPa 3.92 3.29 3.48 3.87 3.27 tensile strength MPa 7.82 4.89 7.39 4.80 6.67 elongation at break % 605 550 560 405 685 Shore A hardness 76 81 81 78 82 Young's modulus MPa 10.2 7.58 8.25 11.6 7.40 TS ² /E MPa 3.18 3.15 6.62 1.98 5.83 in _crit . with ^-i 150 °C 350 7,200 230 195 920

In the examples of the mixture according to the invention, EPDM rubbers of the sequential type can be advantageously used, such as EPDM I with Mooney viscosity ML(1 + 4)/100 °C; 35 or EPDM II with ML(1 + 4); 85.

The mixtures prepared in the kneading device were granulated after a short homogenization. The granulated thermoplastic mixtures did not stick together even without the use of a separator and after long-term storage, nor did their technical properties deteriorate significantly. The granules of the mixture stored at a temperature of 70 °C and a specific pressure of 0.2 MPa for 24 hours remained unglued. Storage of the granulate for 24 months at laboratory temperature also did not lead to the sticking of the granules.

Thermoplastic elastomer mixtures can be further processed by conventional technological processes, such as extrusion or pressing. When extruding the mixture, temperatures of 150 to 190 °C and screws with higher I/D ratios, used for processing plastics, can be advantageously used.

Evaluation of thermoplastic elastomer mixtures on cable insulations prepared according to the invention showed, in addition to the above properties, suitable electrical properties comparable to vulcanized materials - electrical strength up to 25 kV per millimeter, dielectric loss factor at 90 °C 1.0 to 1.5 X 10~ ² , permittivity 2.0 to 4.5. Accelerated temperature aging tests of cable insulations showed their suitability for use for permanent temperature stresses in the range of 70 to 80 °C with the prospect of use primarily for insulations and cable sheaths for voltages up to 6 kV.

In the case of omitting sulfur and the vulcanization accelerator from the composition of the thermoplastic mixture, we obtain materials suitable for application as cable filling mixtures with the possibility of filling to a high degree. The filler can be all common types of fillers used for rubbers up to 800 parts by weight per 100 parts of rubber. Examples of the composition of cable filling mixtures are given in Table 3.

Table 3

Components (weight d.j example no. 11 ’ 12 13 14 SBR rubber 95 100 80 80 EPDM rubber 5 — — — natural rubber — — 20 20 polyethylene with melt index 2.0 — 40 — — polyethylene with melt index 200 20 5 17 17 paraffin 3 1.0 11 11 chalk 600 — 400 500 kaolin — 360 — — ground limestone — — 200 — precipitated limestone — — — 100 adjusting oil 38 35 35

252939

The filling mixtures according to the invention, based on butadiene-styrene rubber or its mixture with ethylene-propylene copolymer or terpolymer or natural rubber and polyethylene, have improved rheological and processing properties and thus better fill the space between the cable cores. They are suitable for cables with both plastic and rubber sheaths and retain their shape to an improved extent even at slightly elevated temperatures.

The mixtures prepared according to the invention have improved technological properties, especially rheological, without significant deterioration of other technical properties of the material. A significant improvement in rheology means a significant increase in the volume production of products and labor productivity. The use of butadiene-styrene rubber in thermoplastic mixtures according to the invention in combination with an ethylene-propylene copolymer or terpolymer also reduces the material costs of production.

Claims (1)

The filler compositions of the present invention, for baseebutadiene-styrene rubber or mixtures thereof with ethylene-propylene copolymer or terpolymer or natural rubber and polyethylene, have improved theological and processing properties and thus better fill the space between the wires of the cable . Appropriate for cables with plastic and rubber coatings and at a slightly elevated temperature retain their shape in an improved manner. The compositions prepared according to the invention have improved technological properties, especially rheological properties, without the significant deterioration of other technical properties of the material. Significant improvement in rheology means a substantial increase in volume production and labor productivity. The use of butadiene-styrene rubber in the thermoplastic compositions of the present invention in combination with ethylene-propylene copolymer or terpolymer also reduces the cost of production. ARTICLE A thermoplastic elastomer composite comprising a synthetic and / or natural rubber, non-crosslinked or partially crosslinked by a sulfur vulcanization system, optionally containing a thiuram to accelerate vulcanization, characterized in that it is composed of an elastomeric component A comprised of between 9.0 and 90 % by weight of styrene-diene rubber containing a maximum of 45% by weight of styrene, from a proportion of ethylene-propylene-diene terpolymer having a range of 40 to 90% by weight of ethylene preferably of a sequential type, and / or mixtures thereof with natural rubber the thermoplastic component B, which consists of 0.3 to 31 weight percent polyethylene with a melt index of 180 to 220 and / or 0.1 to 58 weight percent of polyethylene with a melt index of 0.1 to 20, a filler in the range of 0.0 to 800 parts by weight per 100 parts by weight of rubber.