CS197831B1 - Method for adjusting mechanical properties and size distribution of sintered products of propylene polymers - Google Patents

Abstract

Method for adjusting the mechanical properties and size distribution of injection-molded products made of propylene polymers. The purpose of the invention is to improve the basic mechanical properties of injection-molded products based mainly on isotactic polypropylene while maintaining processing properties. This adjustment can be achieved by adding suitable heterogeneous nucleating agents, inorganic or organic, in an amount of 0.01 to 5.00 wt. d. per 100 wt. d. of propylene polymers. The polypropylene modified in this way will find application primarily in polypropylene processing plants and among consumers of products made of this polypropylene.

Description

The subject of the invention is a technologically simple method of adjusting the size distribution and mechanical properties of polypropylene extrusions, mainly from isotactic polypropylene, by which the processing properties of the polymer are not impaired and its basic mechanical properties are improved.

Isotactic polypropylene, thanks to its favorable processing, physical and mechanical properties, has been used in various areas. However, its wider application is hindered by a wide distribution of dimensions, as well as relatively low impact and notch resistance at low temperatures in products prepared by injection molding technology, especially in those application areas where increased demands are placed on the accuracy of spraying.

The current method of adjusting the impact properties consists either in the copolymerization of polypropylene with ethylene /Mitsubitshi Petrochemioal Co., I/ED., Japan Technology of Block Copolymer 1977/, or in mixing elastomers into the polypropylene melt /Plast, massy 11, 1977/.

Satisfactory results are achieved by the methods mentioned, but at the cost of increasing the financial costs of the production facilities and at the cost of reducing the production capacities of these facilities.

The aforementioned shortcomings can be eliminated by adding an amorphous inactive filler, for example fine glass beads, /Hellerich, Harech, Haule, Werkstoff - Pührer Kunstoffe, Carl Hauser Verlag Munchen Wien, 1975/.

The favorable effect is achieved here at the cost of a significant increase in raw material and production costs, higher wear and tear of processing machines and at the cost of reducing some useful properties of the polymer.

According to another method, the problem of a wide distribution of sprays is solved by means of the technological conditions of injection. This method provides only relatively good results and in most cases does not produce the desired effect on a technological scale for several reasons.

The method of adjusting the mechanical properties and the size distribution of the injected products made of propylene polymers is carried out according to the present invention in such a way that the mechanical properties, . preferably, the notch and impact strength or the size distribution of injected products made of propylene polymers, made of polypropylene are adjusted by adding inorganic or organic heterogeneous nucleating agents, insoluble in propylene polymers with a melting temperature higher than the melting temperature of the "thick j phase" of the propylene polymers and which do not decompose under the processing conditions of the propylene polymers, in an amount of 0.01 to 5.00 wt.d. per 100 wt.d. of propylene.

The procedure according to the present invention therefore consists in modifying the supramolecular structure of the polymer by the effect of suitable structural nucleators in an amount of 0.01 to 5.00% by weight, which results in a narrower distribution of the dimensions of the sprays and in the improvement of the mechanical properties while maintaining the processing properties.

The essence of the influence of these nucleators is in the creation of a large number of crystallization centers, the presence of which causes an increase in the crystallization speed at the same time

197 831 reduction of the size of spherulites and secondary crystallisation.

To monitor the supracrystalline structure of polypropylene samples, it is advisable to use scanning electron microscopy. For quantitative comparisons of individual samples, the average size of spherulites is expressed by the value of the average radius and the number of spherulites per 1 cm of the sample surface. The average radius of the spherulites in the unmodified stained polymer is 865 and the number of spherulites per 1 cm of the sample surface is 42.4. For comparison, in polypropylene modified with 0.75% by weight SiOg, the average radius of spherulites is 405./un and the number of spherulites per 1 cm of the sample surface is 196.2.

The density of the nucleating agents affects not only the size of the spherulites, but also their internal structure, which is also reflected in the mechanical properties of the polymers.

Suitable nucleates are substances of an inorganic and organic nature, insoluble in polypropylene, with a melting point above the temperature of the crystalline phase of polypropylene and which do not change their chemical structure under the conditions of polymer processing.

The SpSsob according to the invention is technically and economically very advantageous, and a modified polymer with the required properties can be easily prepared on machine-technology equipment commonly used in polypropylene factories or in processing plants.

Example 1

Commercial polypropylene Tatrén PD-140 with a melt flow index of 3.30 g/10 min is used to monitor the shrinkage and size distribution of the spatters. and a specific weight of 0.91.10 kg.m. . The modification of the aforementioned basic polymer is carried out by homogenizing polypropylene powder with 0.4 wt. parts of silicon dioxide (Aerosil 200) and subsequent granulation. Injections are prepared on an ENGEL 10/20 machine under the following technological conditions: temperature of the heating zones 210, 220 °C, input power at the nozzle 0.6 A. Work cycle 60 s, injection pressure 700 MPa, temperature 45 °C.

The degree of shrinkage is taken to be the relative change in the size of the injection molding relative to the size of the mold after 46 hours of cooling.

The size of the standard deviation and the coefficient of variation are taken as a measure of the dispersion of dimensions. These values are listed in tab. No. 1:

wrinkled unmodified X and in polypropylene (PP) (%) 0.95 0.047 4.95 shrinking modified polypropylene (%) 1.14 0.031 2.72

where x is the mean value s is the standard deviation v is the coefficient of variation

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Example 2

The basic polymer is used as in example No. 1. Aerosil 200 is used for the modification in an amount of 0.7 wt. parts Shrinkage is evaluated on the quarter-disk model form in the radial and tangential directions. Injected products are prepared on the CS 195 machine under the following conditions: temperature of heating belts 190, 220, 220 °C, nozzle 230 °C, injection pressure 600 MPa, work cycle 20s,

The rate of shrinkage in the radial direction is taken to be the change in the size of the injection in the radial direction related to the size of the mold after 48 hours of cooling.

The rate of shrinkage in the tangential direction is taken to be the change in the length of the circle's circumference relative to the circle's circumference of the injection mold after 48 hours of cooling.

The results are given in Table δ. 2:

unmodified PP X with in radial shrinkage (%) 1.87 0.13 6.95 shrinkage tg. (%) 0.39 0.18 46.15 modifier PP shrinkage radi. (%) 1.64 0.04 2.45 shrinkage tg. (%) 0.18 0.03 16.66

For the polymer modified in this way, they are carried out! measurements of mechanical properties of tensile strength and notch toughness. Tensile strength is measured according to ČSN 64 0605 and notch toughness according to CSN 64 0612. .

The test bodies for these tests are prepared on a CS 195 injection molding machine under the following conditions: heating zone temperatures 190, 200, 220 °C, nozzle temperature 230 °C, control regulator in position 3, injection pressure 1,200 MPa and work cycle 20 s.

Tensile strength is measured on a ZWICK 1 474 universal tearing machine under the following conditions: force sensor indication range 0 to 200 N, testing speed 100 mm/min.

The notch toughness is measured by the Charpy method on the ZWICK 5 102 device. The measurement range is 0.53. Test specimen prepared under the same conditions as test specimens for tensile tests. The measurement results are in tab. No. 3:

Tensile strength [MPa]

Unmodified PP 33.3

Modified PP 35.6

Example 3

The basic polymer is used as in example 1. Hermat Zn MBT (zinc salt of mercaptobenzthiazole) is used for the modification in an amount of 3 wt. parts The notch toughness of the polymer modified in this way is measured by the method given in example 2. The notch toughness of the unmodified polymer is 3.6 kJ/m, and the modified one is 5.0 kJ/m.

Notched ductilityV. [kJ/m^J

3.6

4.7

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Claims (1)

OBJECT OF THE INVENTION Process for adjusting the mechanical properties and size distributions of injection molded products of propylene polymers, characterized in that the mechanical properties, preferably notched and impact strength, or dimensional distribution of the injection molded products of propylene polymers, preferably polypropylene, are modified by adding heterogeneous organic nucleating agents % insoluble in propylene polymers, with a melting point greater than the melting point of the crystalline phase of the propylene polymers and not decomposing under propylene polymer processing conditions, in an amount of 0.01 to 5.00 parts by weight per 100 parts by weight of propylene polymers.