CS243313B1 - A method for producing a composite material by compounding polypropylene - Google Patents

Abstract

The invention relates to a method for producing a composite material by compounding polypropylene or copolymers of propylene with ethylene, calcium carbonate, organic peroxide, or other processing additives. The kneading is carried out in the presence of a sterically hindered phenol substituted with an aliphatic substituent with at least 18 carbon atoms. A material with good flowability for the production of articulated moldings is obtained.

Description

(54) Method of producing composite material by compounding polypropylene

The invention relates to a method for producing a composite material by compounding polypropylene or copolymers of propylene with ethylene, calcium carbonate, organic peroxide, or other processing additives. The kneading is carried out in the presence of a sterically hindered phenol substituted with an aliphatic substituent with at least 18 carbon atoms. A material with good flowability for the production of articulated moldings is obtained.

The invention relates to a method of producing composite materials based on polypropylene or its copolymers, calcium carbonate, organic peroxide and possibly other processing additives.

For the production of articulated injection-molded products characterized by high rigidity, dimensional stability, good toughness and at the same time good flowability, it is advantageous to use polypropylene whose structure has been chemically modified by degradation in the melt.

When mixing pre-ground polypropylene with inorganic filler, which is carried out in continuous kneaders or twin-screw mixing extruders, it is necessary to maintain the melt temperature relatively precisely within a narrow range, where the melt has sufficient viscosity required for efficient energy transfer from the kneading device to the material, which is necessary to achieve the necessary dispersion of the filler.

Therefore, it is more advantageous to start from high molecular weight polypropylene /or its copolymers/ and to degrade polypropylene only in the presence of a filler. Compounding polypropylene with an organic peroxide additive is described, for example, in JA 131032.

If one proceeds according to the aforementioned Japanese invention, which mixes four components: a/ polypropylene, b/ filler, c/ organic peroxide, d/ lubricant formed by an organic fatty acid, its salt or ester, the resulting material has uneven properties and is unsuitable for practical applications. The reason is the poor reproducibility of the formation of the necessary free radicals in the melt and their inhomogeneous distribution.

When dosing organic peroxide into a mixing extruder, it is necessary to ensure that its molecular dispersion in the melt occurs before its decomposition occurs. Even if a peroxide is used that begins to decompose rapidly after reaching a temperature of 180 to 220 °C, the peroxide remains present in the form of associates in the environment of non-polar polyolefins and its uniform molecular dispersion is not achieved.

Reproducible rates of free radical generation, and therefore reproducible properties of the final composite materials, can be achieved if, in addition to peroxide, a suitable modifier is added, which has a triple function:

a/ prevents unwanted chain decomposition of peroxide associates, which are the cause of the unreproducibility of previously known processes b/ contributes to the rapid and homogeneous dispersion of peroxide in the melt o/ ensures the necessary thermo-oxidative stabilization of the final material.

The subject of the invention is a method of producing a composite material by compounding polypropylene or propylene copolymers with ethylene, calcium carbonate, organic peroxide and optionally other processing additives, in which polypropylene or its copolymer with a flow index lower than 4g/10 min /at 230 °C, load 21 N/ is kneaded in a continuous mixing extruder with micro-ground limestone with an average particle size of up to 5 tons in the presence of an organic peroxide with a half-life at 200 °C of 10 to 30 seconds and a modifier containing a sterically shielded phenol substituted with an aliphatic substituent with at least 18 carbon atoms.

The starting polypropylene may be a homopolymer or copolymer of propylene with ethylene containing less than 5% by weight of ethylene.

When melting high-molecular polypropylene with a flow index lower than 4g/10 min /at 230 °C load 21 N/, we obtain a viscous melt in a wide temperature range, in which, due to the efficient transfer of energy from the kneading screw, the filler is easily dispersed without the need for very precise temperature control.

A suitable inorganic filler is characterized both physically and chemically. The physical characterization concerns the size of the particles, whose diameter is optimally in the range of 1 to 5/ton and whose sorting is carried out in such a way that fractions larger than 10, respectively. 20 _< um are removed. The chemical characterization concerns the absence of strongly acidic surface centers causing non-radical ineffective decomposition of peroxides.

An example of fillers with a high concentration of acid centers are aluminosilicates. However, even micro-ground limestone always contains larger or smaller concentrations of impurities that can be used in the ineffective decomposition of peroxides into alcohols and ketones.

In practice, this means that the concentration of peroxide required to chemically modify polypropylene in the presence of a filler will be greater than without its presence and will depend on the purity and concentration of the given filler.

The choice of a suitable peroxide - a free radical generator - is defined in such a way that during the kneading process, on the one hand, the peroxide must completely decompose, on the other hand, the peroxide must not decompose prematurely, that is, before the polymer melts. For reasons of work safety, it is advantageous to apply the necessary peroxide to the filler in advance. Its optimal concentration ranges from 0.01 to 0.5% by weight of the final composite material.

Examples of suitable commercial peroxides meeting these conditions are given in the table: .

Peroxide Half-life /s/ at temperature

180°C 200°C 220°C Dicumyl peroxide 55 15 4 2,5-dimethyl-2,5-di-tert. butyl peroxyhexane /1/ 70 18 5 tert.butyl-cumyl-peroxide 70 20 . 5 Bis/tert.butyl peroxy- isopropyl/benzene 90 25 7

As modifiers, it is possible to use substances that are capable of reacting rapidly with radicals formed during peroxide decomposition and with other radicals formed on the polymer chain. As modifiers, substances having fully or partially shielded phenolic groups can be used.

The essential condition is the presence of an aliphatic chain with at least 18 carbon atoms or longer, which allows for rapid homogeneous dispersion of the peroxide used in the polypropylene melt.

Examples of suitable modifiers are:

- octadecyl ester of /3,5-di-tert.butyl-4-hydroxyphenyl/propionic acid /11/.

- 2,6 dimethyl-4-oligopropenyl phenol /111/.

The optimal concentration of modifiers is always greater than the peroxide concentration used. The advantage of the new process is the possibility of wide control of the properties of the final composite material using a single type of starting polypropylene.

The following examples will further illustrate the nature of the invention. The parts and percentages given in the examples are by weight. The flow index was determined according to ČSN No. 640 861.

Example 1

The following was simultaneously dosed into the hopper of the Werner-Pfleiderer ZSK 53 twin-screw mixing extruder:

2433X3 parts of polypropylene /powder homopolymer characterized by a melt index of 0.8 g/10 min at 230 °C/

40 parts of micro-ground limestone /characterized by an average particle size of 2.7 <um and sorted below the elbow/, provided with a layer of 0.3% stearic acid

0.11 parts of peroxide I.

0.18 parts of modifier II.

The latter two components were dosed together as a common solution.

Kneading was carried out at a temperature of 230 °C, the residence time of the melt in the extruder was 150 seconds. The mixture was extruded in the form of a string and chopped into granules, from which test specimens were prepared by injection molding at a melt temperature of 250 °C.

Example 2

Conditions as in Example 1, polypropylene homopolymer characterized by a melt index of 2.8 g/10 min was used, the following additives were used:

0.012 parts of peroxide I.

} 0.022 parts of modifier III.

Example 3

Conditions as in Example 1, using a propylene-ethylene copolymer /98/2/ characterized by a melt flow index of 0.67 g/10 min.

The following ingredients were used:

0.16 parts of peroxide I.

0.26 parts of modifier II.

Attached

The conditions and polymer used were as in Example 3. The following additives were used:

0.10 parts of peroxide I.

0.18 parts of modifier III.

The processing and mechanical properties of the materials prepared according to examples 1 to 4 are characterized by the table:

Claims (1)

OBJECT OF THE INVENTION * A method for producing a composite material by compounding polypropylene or copolymers of propylene with ethylene, calcium carbonate, organic peroxide, or a carbon black. Other processing ingredients, characterized in that the polypropylene or copolymer having a flow index of less than 4.0 g / 10 min, at a load of 21 N at 230 ° C, is kneaded in a continuous micronized limestone mixing extruder with an average particle size of up to 5 µm in presence of an organic peroxide having a half-life at 200 ° C of 10 to 30 seconds; and a modifier comprising a sterically shielded phenol substituted with an aliphatic substituent of at least 18 carbon atoms.