CS246636B1 - A method for producing a composite material - Google Patents

Abstract

The solution relates to a method for producing a composite material based on polypropylene, polyethylene, calcium carbonate, organic peroxide and optionally processing additives. Polypropylene with a flow index lower than 4 g/10 min is kneaded in the first zone of a two-belt mixing extruder with a micro-ground blank in the presence of organic peroxide and modifiers containing functional groups capable of radical transfer and an aliphatic or cycloaliphatic chain for a period corresponding to at least three half-lives of the decomposition of the peroxide used under kneading conditions, and in the second zone, high molecular weight polyethylene is dispersed in the melt. A material with good mechanical properties and good processability is obtained.

Description

BACKGROUND OF THE INVENTION The present invention relates to a process for the production of composite materials based on mixtures of polypropylene with polyethylene and optionally copolymers of ethylene with propylene and calcium carbonate, which makes it possible to control their processing and utility properties directly in the extruder.

For many applications, for example in the automotive industry, readily processable thermoplastic materials having both high rigidity and toughness are required.

According to AO 197.043, in the presence of inorganic fillers, for example micronized limestone, polypropylene / polyethylene mixtures can be prepared which have high rigidity and toughness over a wide temperature range.

However, a disadvantage of these materials based on conventional polypropylene injection types is the relatively low flowability, which makes it difficult to inject rugged products.

Compounding of polypropylene, copolymers of propylene with ethylene, and mixtures thereof with inorganic fillers with an organic peroxide additive is described in JP 55 131032. However, when the Japanese patent is described, it discloses four components: a / polypropylene, copolymers or mixtures, b / filler, c / organic peroxide, a d / lubricant formed by an organic fatty acid, its salt or ester, gives the material non-reproducible properties and sometimes unsuitable for practical applications. This is due to poor controllability of the rate of formation of the necessary free radicals in the melt and their homogeneous distribution.

When dosing the organic peroxide into the mixing extruder, it must be ensured that its molecular dispersion in the melt occurs before significant decomposition occurs.

Although a peroxide that rapidly decomposes above the melting point of polypropylene is used, the peroxide remains present in the form of associates in the non-polar polyolefins and does not achieve uniform molecular dispersion.

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

a) ensures rapid and homogeneous dispersion of peroxide in the melt b / prevents undesirable chain decomposition of peroxide associates, which causes non-reproducibility of the process performed according to JP 55-131032.

c / provides the necessary thermo-oxidative stabilization of the final material.

SUMMARY OF THE INVENTION The present invention provides a process for the manufacture of composite materials based on polypropylene or copolymers of propylene with ethylene, polyethylene or copolymers of ethylene with alpha-olefins, calcium carbonate, organic peroxide and optionally processing additives, wherein the polypropylene or copolymer of propylene with ethylene with a flow index of less than 4. g / 10 min. knead in the first zone of a dual-band mixer with micronized limestone in the presence of an organic peroxide and a modifier containing functional groups capable of radical transfer and an aliphatic or cycloaliphatic chain for at least three half-lives of the peroxide used under kneading conditions; or a copolymer of ethylene with alpha-olefins having a flow index of less than 1 g / 10 min.

The starting polypropylene may be either a homopolymer or a random or block copolymer of propylene with ethylene containing less than 5% by weight. ethylene, characterized by a flow index of less than 4 g / 10 min.

The second component of the polymer matrix is polyethylene, which may be a homopolymer or copolymer of ethylene containing a maximum of 5% alpha-olefin, characterized by a flow index of less than 1 g / 10 min.

The process itself is preferably conducted in such a way that polypropylene with micronized limestone is kneaded in the first zone of the extruder mixing extruder in the presence of an organic peroxide and modifier and only polyethylene is metered into the second zone of the extruder.

In the first stage of the process, the mechanical energy needed to overcome the attractive forces between the filler particles must be supplied to disperse the filler. When the mixture is heated, which is largely due to the frictional heat, the polymer goes into a melt state, and at the same time the added peroxide begins to decompose into free radicals which cause a controlled reduction in the molecular weight of the polypropylene.

The melt temperature in the first zone of the mixing extruder will control it so that the bulk of the peroxide used is decomposed before the polyethylene is added to the filter. T «means that the residence time of the melt in the first zone of the extruder must correspond to at least 3 half-lives of the peroxide used.

Otherwise, the use of a high molecular weight polyethylene additive can significantly increase polyethylene cross-linking and result in the composite material being unprocessable. Conversely, very poor polyethylene crosslinking induced by the decomposition of residual peroxide may be desirable in many cases to achieve optimal properties.

The process thus offers the possibility of very fine regulation of the final properties of the composites over a wide range of monitored parameters.

The half-lives of some suitable peroxides are shown in Table I .;

Table I

Half-lives of some peroxides.

Peroxide Half-life (s) at temperature 180 ° c 200 ° C 220 Dikumylperoxid 55 15 Dec - 2,5-dimethyl-2,5-di-t-butylperoxyhexane (1) 70 18 5 t-butyl cumyl peroxide 70 20 May 5 Sis (t-butyl-peroxy-isopropyl) benzene 90 25 7

For example, if a mixing extruder is used in which the residence time of the material in the first zone, i.e. until the second inlet zone, is 25 s, it is clear from the table that the melt temperature should be controlled to reach a minimum of 220 ° C.

The effect of the modifier jc can be explained as follows:

The breakdown of peroxide R-O-O-R in the presence of a modifier produces stable radicals by transfer, so that non-reproducible chain breakdown of other peroxide molecules does not occur.

Suitable modifiers include, on the one hand, aliphatic or cycloaliphatic chains ensuring good solubility in the environment of nonpolar polyolefins, and partially or fully shielded phenolic functional groups, ensuring the conversion of reactive radicals into stable radicals.

Examples of suitable modifiers include:

2,6-dimethyl-4-oligopropenyl-phenol

2,6-di-tert-butyl-4-octadecylphenol

2-phenyl / 3 ', 5'-tert-butyl-4'-hydroxy / propionic acid 2,6-di-tert-butyl-4-ethylcyclohexylphenol stearyl ester.

The required amount of polyethylene is fed into the second zone of the mixing extruder. To achieve high toughness, it is important that the polyethylene used has a higher molecular weight than the resulting modified polypropylene.

A suitable type of micronized limestone is a finely dispersed powder of high chemical purity, characterized by an average particle size in the range of 1 to 3 µm sized to contain no particles larger than 10 µm.

It is expedient to treat the filler with a semipolar substance forming on the one hand a bond with the surface of the filler, on the other hand a bond with the polymer matrix. Examples of suitable substances are higher fatty acids and their esters. The surface treatment of the filler is not a necessary condition, but in its use the energy consumption for the dispersion of the filler is lower.

The following examples illustrate the invention in more detail. The parts and percentages given in the examples are by weight.

Example 1

Into the first inlet of the continuous kneader Buss type MDK 140/11 D was dosed:

35 parts of isotactic polypropylene (homopolymer) characterized by a flow index

X.T.23O 0.7 g / 10 min.

40 parts of micronized limestone Durcal 2 (manufactured by Pluess-Staufer), characterized by an average particle size of 2.7 µm and sorted below 10 µm, which was coated with 0.3% by weight of stearic acid, 0.18% by weight of peroxide (1) (and 0.30% by weight 2,6-dimethyl-4-oligopropenylphenol) (11).

The residence time of the material in the first zone of the kneader was 25 s, the temperature in this zone being increased to 225 ° C.

25 parts of an ethylene-3-butylene copolymer characterized by a flow index IT _go w of 0.21 g / 10 min were fed into the second inlet of said kneader.

The produced granulate was prepared by injection molding a test piece.

The property / together with the materials prepared according to other examples are shown in Table XI.

Example 2

Procedure and Materials Used as in Example 1. 25 parts of polypropylene and 60 parts of micronized limestone treated as in Example 1 were fed into the first inlet. 15 parts of ethylene-3-butylene copolymer were fed into the second inlet.

• Example 3

Procedure and materials used as. in Example 1. 48 parts of polypropylene and 40 parts of treated micronized limestone were metered into the first inlet. 12 parts of polyethylene, characterized by an IT _igo «« 0.3 g / 10 min, were fed into the second inlet.

He attaches

30 parts of polypropylene and 20 parts of micronized limestone with 0.2% by weight peroxide I and 0.33% by weight modifier II were fed into the first inlet of the continuous kneader.

50 parts of polyethylene were fed into the second inlet.

Table II

Properties of the materials produced according to Examples 1 to 4

Property 1 Example # 2 3 4 Flow index ^.Τ. ^ θ / g / 10 min / 1.9 1.4 4,5 0.78 Modulus of elasticity (GPa) 2.5 4.6 2.7 1.5 -2 Notch toughness /kJ.m / 18 14 10 not broken

Claims (1)

Process for the production of a composite material based on polypropylene or a copolymer of propylene with ethylene, polyethylene or a copolymer of ethylene with alpha-olefins, calcium carbonate, organic peroxide and optionally processing additives, characterized in that polypropylene or copolymer of propylene with ethylene with a flow index of less than 4 g / 10 min. knead in the first zone of a dual-band mixer with micronized limestone in the presence of an organic peroxide and a modifier containing functional groups capable of radical transfer and an aliphatic or cycloaliphatic chain for at least three half-lives of the peroxide used under kneading conditions and dispersed in the latter polyethylene or a copolymer of ethylene with alpha-olefins with a flow index of less than 1 g / 10 min.