CS224725B1 - Method of manufacture of tough polypropylene on single screw extruder - Google Patents

Description

SUMMARY OF THE INVENTION The present invention relates to a process for preparing tough polypropylene on a single screw extruder with a two-stage screw and a granulation device which is intended for special applications where good toughness even at low temperatures is required, e.g. ski boots, safety bindings, etc.

Isotactic polypropylene is a widespread plsstomer due to its mechanical properties. An undesirable phenomenon in this otherwise high-quality polymer is a significant decrease in the values of mechanical properties at lower temperatures β to below 4 - 10 ° C. A negative change in properties is prevented by the fact that the basic isotactic polymer is modified by the addition of special elastomeric substances, in particular those of propylene linen rubbers, which are themselves inherently high resilient and with which polyjoprene filaments form micro-heterogeneous mixtures whose properties are proportional to the elastomeric component content. , the degree of its dispersion and the thermooxidation and photooxidation stability of the prepared mixture.

These special mixtures have so far been prepared in essentially two ways. Either multi-screw machines specially designed for this purpose, eg twin-screw continuous kneading extruders, can be used to blend the base polymer with the elastomeric component in which pressure and shear conditions can be developed which guarantee perfect homogenization of both components at operating temperatures up to 210 ° C. to avoid distortion during melt mixing

2247 25 temperature sensitive rubber components. The second method of producing tough polypropylene blends is also a two-stage process and does not preclude the use of a single wall granulating extruder.

For perfect blending of both components, however, a melt discontinuous kneader or a conventional rubber kneader is used, in which a homogeneous melt is prepared at temperatures of 180-190 ° C, which in the second stage is only granulated on a conventional granulation device. The relatively long residence time of the masses in the kneader (10-15 min) does not allow the use of higher operating temperatures during mixing, since the rubber component could not be controlled at a relatively long residence time.

The methods for preparing tough polypropylene are very energy and time consuming processes. First of all, from an energy point of view, the use of special kneaders represents a considerable load, since the entire two-stage process is in the molten state. Another disadvantage is the relatively long thermal stress of the rubber component.

We found that a sufficiently tough polypropylene can be manufactured _y no jednoěnekovém extruder with a special two-stage auger saving energy and time. The novel process for producing a tough polypropylene on a single wall extruder differs substantially from the above-mentioned methods and eliminates some of their disadvantages and takes advantage of the fact that the elaetomeric component, e.g. The marked increase in temperature during mixing, which is achieved by friction in the material and not by the heat input from the outside, results in a radical change in the rheological properties of the melt and allows perfect mixing of both components in substantially shorter time and less mechanical stress. It has been found that, under the operating conditions below, a period of 20-40 seconds is sufficient to mix the two components homogeneously, i.e. the time that the mass is held in the melting and subsequent kneading zone of a single wall extruder.

According to the invention, the process for producing a tough polypropylene on a one-piece extruder consists in mixing the granulated polypropylene ae in a legal phase and a rubber modifier and longer free-flowing additives in a two-cone mixer at ambient temperature and a homogeneously homogeneous mixture. machines equipped with a two-stage screw and a compression ratio of 2,0 - 4,0 in the first stage and 1,5 - 3,0 in the second stage, with a total L / D value greater than 25, with a material in the melting zone of 16-18 D at temperatures of individual zones 30-50 / 200-250 / 200-230 ° C first melts and then in the kneading zone of the screw of 8-10 D at temperatures of individual sections 170-190 / 200-220 / 200-260 ° C perfectly bend through a screw tempered to 90-180 ° C, at 60-120 rpm, which delivers the amount of energy needed for the corresponding melting delay time 15-40 seconds to uniformly distribute the modifying component and achieve the desired properties, compressing the homogenized tevenine to a pressure of 8-12 MF and passing through a sieve and holes of 150 to 850 mm diameter and a 50-80 ° C water-cooled granulating head, and then chopped into choppers of the desired size with a chopping machine whose knives ae rotate at a speed of i000-1,600 rpm.

Polypropylene-modified ethyl-propylene-diene rubber produced in this way, has a high homogeneity and a flow properties corresponding to the properties of the same and produced with a double-stranded special extruder at a lower specific energy consumption.

The invention is illustrated by the following examples:

Example

In a two-cone mixer it was at room temperature for 30 min. mixed 3 000 kg of isotactic polypropylene, 1 000 kg of ethyl 1-propylene-diene rubber β 40 kg of carbon black. The mixture thus prepared was continuously metered into a single screw extruder and a two-stage screw with a total I / D ratio greater than 25, where it was granulated under the following conditions:

temperature - extruder cylinder zones: 40/239/216/187/212/225 ° C in direction of extruder screw hopper: 140 ° C mower water: 65 ° C extruder screw speed: 62 min. * ^- no pressure extruder head: 8 MPa mower blade speed: 1,250 min. '' ^L

The granulate produced by this process was highly homogeneous and had satisfactory mechanical properties even at low temperatures, as can be seen from Table 1. The power consumption was 0.25 kW / kg of line power.

Table 1

Mechanical properties of granulate property unit granulate according to example 1 according to example 2 produced on a twin screw machine

tensile strength MPa 25.1 25.5 25.5 ductility % 90 80 80 notched - 40 ° CkJ / m ² 7.5 6.8 7.1 toughness r 20 ° CkJ / m ² 10.0 10.5 8.6 hardness ° F D 58 58 58 thermal resistance Noc: 2 ° C 51 53 49 ISO 75 B-modulus in bend MPa 950 1 050 1 000 - point flux index g / 10 min. 2.1 2.2 1,8

230 [deg.] C .; 21.2 N

From the values shown in Table 1 it is clear that the granulates prepared by the PV process are practically equivalent to the granules prepared on an investment-intensive special twin screw machine with energy consumption that is lower compared to a twin screw extruder

Claims (1)

Process for producing tough polypropylene on a single screw extruder, characterized in that the granulated polypropylene is blended in legal phase with a rubber modifier with other free-flowing additives in a two-cup mixer at ambient temperature and the resulting homogeneous mixture is continuously fed into a single screw extruder equipped with two stages a screw and a compression ratio of 2.0 to 4.0 in the first stage with 1.5 to 3.0 in the second stage, wherein the material is in a melting zone of 16 to 18 D at temperatures of 30 to 50, 200 to 250, 200 to 230 ° C first melted and then in the kneading zone of the worm with a length of 8 to 10 D at temperatures of the sections 170 to 190, 200 to 220, 200 to 260 [deg.] C. was completed by kneading the screw at 90 to 180 [deg.] C., at 60 to 120 rpm at a residence time of 15 to 40 seconds, then the homogenized melt was compressed to 8 to 12 MPa and passed through a 150 to 850 mm and a 50 to 80 ° C chilled water cooling head, and chopped at a speed of 1,000-1,600 rpm per minute, not granules. Price: 2,40 Kčs