RU2441028C2 - Propylene polymers - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to propylene polymers, having specific values of total comonomer content and melting point. Described is a propylene polymer having total content of links obtained from ethylene of 4.5-6.0 wt %. The polymer has melting point of 148°-160°C. The invention also describes a gas-phase polymerisation method for obtaining a propylene polymer, a method of producing moulded articles and a moulded article obtained using blow extrusion.

EFFECT: obtaining a propylene polymer having good balance of physical and mechanical properties which can improve efficiency of extrusion methods.

6 cl, 2 tbl, 3 ex

Description

The present invention relates to propylene polymers having specific values of the total comonomer content and melting point, to articles made therefrom, in particular to blow molded products, and to methods for producing said propylene polymers.

It is widely known in the art that propylene copolymers can be used in extrusion processes and, in particular, for the production of blow molded extruded products due to the good balance of their physical and mechanical properties. Propylene copolymers commonly used in extrusion processes have acceptable stiffness, good impact properties, especially at low temperatures, and good optical properties, i.e. low haze values. The desired balance of properties of propylene copolymers suitable for extrusion methods is usually obtained by carefully dosing the content of propylene copolymer comonomers. An increase in the content of comonomer typically present in said copolymers leads to an improvement in the impact resistance of the copolymers, while at the same time inevitably impairing the stiffness; a decrease in the comonomer content inevitably leads to an improvement in stiffness and a decrease in impact resistance. A change in the comonomer content also has a strong effect on the melting point and crystallization of propylene copolymers, Tm and Tc decrease with increasing comonomer content and increase with decreasing comonomer content. For example, it is known from International Patent Application WO02 / 051912 that propylene copolymers having a total ethylene content of 1.4% by weight can have a melting point of more than 161 ° C, and the unpublished patent application PCT / EP2006 / 062152 describes propylene copolymers -ethylene having an ethylene content in the range of 4.5-7.0 wt.% and a melting point lower than 143 ° C. Propylene polymers having an ethylene content of about 5.0 wt.% And a higher melting point are known from European patent EP1206499, in the name of the same applicant. The melting points described in Examples 1 and 2, however, relate to propylene polymers in which nucleation is initiated using 2000 ppm. di-benzylidene sorbitol.

In some extrusion methods, such as blow molding, the performance is strongly influenced by the cooling step, and the melting and crystallization temperatures of the resin are therefore critical to productivity.

An object of the present invention is to provide a propylene polymer having a good balance of physical and mechanical properties that can improve the performance of extrusion processes, in particular blow molding methods.

For this reason, the present invention provides propylene polymers having a total content of units derived from at least one linear or branched alpha olefin having 2-8 carbon atoms other than propylene, in the range from 4.5 to 6, 0 wt.%, Preferably from 4.7 to 5.5 wt.%, More preferably from 4.8 to 5.2 wt.%, And the melting temperature Tm (measured using DSC (differential scanning calorimetry in a polymer of reactor), ranging from 148 ° C to 160 ° C, preferably from 150 ° C to 158 ° C, more preferably from 153 ° C about 156 ° C. The values of Tm, characterizing the propylene polymers according to the invention must be measured for "polymer reactor", i.e. for a polymer as such without adding any additives or fillers, in particular without the addition of nucleating agents.

Propylene polymers may additionally have at least one feature from the following plurality:

- melt flow rate (MFR), in the range from 0.1 to 25 g / 10 min, preferably from 0.5 to 5 g / 10 min, and more preferably from 1.2 to 2.5 g / 10 min . The desired MFR can be obtained directly for polymer grades “from the reactor”, and in particular for MFR greater than 5 g / 10 min, it can be obtained by lightly cracking the grades of “reactor” in accordance with known technologies.

- The xylene soluble fraction at 25 ° C is lower than 15 wt.%, More preferably lower than 12 wt.%; and / or

- The value of the polydispersity index (PI) in the range from 3.0 to 9.0, more preferably from 4.0 to 6.0.

At least one alpha olefin is preferably selected from the group consisting of ethylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 4-methyl-1-pentene, ethylene is particularly preferred.

The propylene polymers according to the invention can be obtained by polymerizing propylene and at least one linear or branched alpha-olefin having from 2 to 8 carbon atoms other than propylene, using a gas phase polymerization process carried out at least two interconnected polymerization zones, the method includes introducing propylene and at least one linear or branched alpha-olefin having 2-8 carbon atoms other than propylene into said polymerization zones and, in the presence of a highly stereospecific heterogeneous Ziegler-Natta catalyst system under the reaction conditions, and collecting the polymer product from these polymerization zones, in this method the growing polymer particles flow up through one of these polymerization zones (vertical column) under conditions of rapid fluidization (formation of a fluidized bed ), leave the specified vertical column and enter another polymerization zone (pipe with a downward flow), through which they flow down under the action of gravity, leave the decree downstream pipe and is introduced back into the vertical column, thereby establishing a polymer circulation between the vertical column and the downward pipe, and means are provided that can completely or partially prevent the gas mixture present in the vertical column from entering the pipe with a downward flow, and a gas and / or liquid mixture having a composition different from the gas mixture present in the vertical column, is introduced into the pipe with a downward flow, the method further from ichaetsya that:

- the ratio of the introduced monomers C _x ^- / (C _x ^- + C ₃ ^- ) for the vertical column is in the range from 0.050 to 1,000 mol / mol, preferably from 0.055 to 0.070 mol / mol.

In the first polymerization zone represented by a vertical column polymerization method, the growing polymer flows under conditions of rapid liquefaction. Both polymerization zones are interconnected accordingly. The growing polymer and the gaseous mixture leaving the vertical column are transferred to the separation zone, while the gaseous mixture is separated from the growing polymer. From the separation zone, the growing polymer enters the second polymerization zone, represented by a downflow pipe, where the growing polymer flows in a compacted form by gravity. The growing polymer particles leave said second polymerization zone and are reintroduced into said first polymerization zone, thereby establishing polymer circulation between the two polymerization zones. Material balance is maintained through the introduction of monomers and catalysts and the release of polymer powder. Typically, rapid liquefaction conditions in the first polymerization zone are established by introducing a gas mixture of monomers below the point of reintroduction of the growing polymer into said first polymerization zone. The rate of transported gas injected into the vertical column should be higher than the rate of transfer under operating conditions, and depends on the gas density and particle size distribution of the solid product. Preferably, it is between 0.5 and 15 m / s, more preferably between 0.8 and 5 m / s. Typically, various catalyst components are introduced into the vertical column through a line, which is preferably placed at the bottom of the vertical column. However, they can be introduced at any other point in the vertical column, as well as at any point in the downflow pipe or mutual connection sections. The entry of the gas mixture, which is separated from the circulating solid product in the separation zone, into the downflow pipe should be completely or partially prevented. This can be achieved by introducing gas and / or liquid into the downward flow pipe through a line placed at the corresponding point of said downflow pipe, preferably in its upper part, through one or more injection lines. The gas and / or liquid mixture, which must be introduced into the pipe with a downward flow, must have an appropriate composition different from the composition of the gas mixture present in the vertical column. The specified gas and / or liquid mixture partially or completely replaces the gas mixture captured by the particles of the polymer entering the pipe with a downward flow. The flow rate of these gaseous starting materials can be controlled in such a way that there is a gas stream in countercurrent with the flow of polymer particles in the downward flow pipe, in particular in its upper part, thus acting as a barrier to the gas mixture coming from a vertical column that is trapped between polymer particles. According to a particularly preferred embodiment, a gas and / or liquid mixture of a different composition, which is to be introduced into the downflow pipe, is introduced in partially or completely liquefied form. More preferably, said gas and / or liquid mixture consists of liquefied propylene.

Optionally, one or more inert gases, such as nitrogen or an aliphatic hydrocarbon, are maintained in the polymerization zones in such quantities that the sum of the partial pressures of the inert gases is preferably between 5 and 80% of the total gas pressure. Operating parameters, such as, for example, temperature, are those that are common in gas phase olefin polymerization processes, for example, the temperature is between 50 ° C and 120 ° C, preferably from 70 ° C to 90 ° C. The method can be carried out at a working pressure in the range from 0.5 to 10 MPa, preferably in the range from 1.5 to 6 MPa. A polymerization device suitable for carrying out the process is described in detail in International Patent Application WO00 / 02929, in particular in FIG. 4. The molecular weight distribution of the growing polymers can be controlled by the content of the respective specific molecular weight regulators, in particular hydrogen, in various proportions in at least one polymerization zone, preferably in a vertical column.

To obtain the propylene polymers according to the present invention, the polymerization method must be carried out by introducing into a vertical column a mixture of monomers, characterized by the ratio of the introduced monomers C _x ^- / (C _x ^- + C ₃ ^- ), enclosed in a narrow range from 0.050 to 1,000 mol / mol, preferably from 0.055 to 0.070 mol / mol, where C _x ^is at least one alpha olefin having 2-8 carbon atoms other than propylene used as a comonomer to produce propylene polymers, and C ₃ ^is propylene. The Tm value of the polymer powders released from the polymerization reactor is constantly monitored by DSC measurements.

In accordance with a preferred embodiment, the method is carried out so that the mass content in the vertical column is in the range from 30 to 50 wt.%, More preferably from 35 to 45 wt.%, And the mass content in the downstream pipe is within from 50 to 70 wt.%, preferably from 55 to 65 wt.%. Mass content, either in a vertical column or in a pipe with a downward flow, is defined as the amount of polymer mass present in one polymerization zone; "relative mass content" is expressed as the mass percentage with respect to the total amount of polymer present in the reactor, that is, in the vertical column and in the downflow pipe. The amount of polymer present in the polymerization zones of the reactor is measured in accordance with known methods. The mass content is continuously monitored and maintained within the above ranges during the polymerization reaction.

In accordance with a specific embodiment of the present invention, the propylene polymer may comprise a mixture of propylene copolymers, said copolymers having different comonomer contents. When the propylene polymers of the present invention are obtained in accordance with the polymerization method described above, the propylene polymer may contain (percent relative to the sum of components (I) and (II)):

(I) 30-50 wt.%, More preferably 35-45 wt.%, A propylene copolymer with at least one linear or branched alpha-olefin having from 2 to 8 carbon atoms other than propylene specified the copolymer contains from 3.6 to 15.0 wt.%, preferably from 6.0 to 12.0 wt.%, units derived from alpha-olefin (relative to component (I)); and

(II) 50-70 wt.%, More preferably 55-65 wt.%, A propylene copolymer with at least one linear or branched alpha olefin having from 2 to 8 carbon atoms other than propylene, said copolymer contains from 0.01 to 3.5 wt.%, preferably from 0.9 to 2.0 wt.% (relative to component (II)) units derived from alpha-olefin,

where the amount of component (I) corresponds to the relative mass content in the vertical column and the amount of component (II) corresponds to the relative mass content in the downstream pipe.

Preferably, components (I) and (II) contain the same alpha olefin, said alpha olefin is preferably selected from the group discussed above.

Ziegler-Natta catalysts suitable for the preparation of propylene polymers of the present invention comprise a solid catalyst component comprising at least one titanium compound having at least one titanium-halogen bond and at least one donor compound electron (internal donor), both are on a carrier of magnesium chloride. Ziegler-Natta catalyst systems further comprise an organic aluminum compound as the main cocatalyst and, optionally, the compound is an external electron donor.

Suitable catalyst systems are described in European Patents EP45977, EP361494, EP728769, EP 1272533 and International Patent Application WO00 / 63261.

Preferably, the solid catalyst component comprises Mg, Ti, halogen and an electron donor selected from esters of mono- or polycarboxylic acids, which can be either aliphatic or aromatic. Among the aliphatic acid esters, malonates, glutarates and succinates described in International Patent Application WO00 / 63261 are preferred. Among the aromatic acid esters, benzoates and phthalates described in EP45977 and in particular either diisobutyl phthalate or dihexyl phthalate or diethyl phthalate and mixtures thereof are preferred.

According to a preferred method, a solid catalyst component can be obtained by reacting a titanium compound of the formula Ti (OR) _ny X _y , where n is the valence of titanium and y is a number between 1 and n, preferably TiCl ₄ , with chloride magnesium obtained from an adduct of the formula MgCl ₂ · pROH, where p is a number between 0.1 and 6, preferably from 2 to 3.5, and R is a hydrocarbon radical having 1-18 carbon atoms. The adduct can be suitably prepared in spherical form by mixing alcohol and magnesium chloride in the presence of an inert hydrocarbon immiscible with the adduct, working under stirring conditions at the melting point of the adduct (100-130 ° C). The emulsion is then quickly quenched, thereby causing the adduct to solidify in the form of spherical particles. Examples of spherical adducts prepared in accordance with these procedures are described in US Pat. No. 4,399,054 and US Pat. No. 4,469,648. The adduct thus obtained can directly interact with the Ti compound or it can first undergo thermally controlled dealcoholation (80-130 ° C) with in order to obtain an adduct in which the number of moles of alcohol is generally lower than 3, preferably is in the range between 0.1 and 2.5. The reaction with the Ti compound can be carried out by suspending the adduct (dealcoholized or as is) in cold TiCl ₄ (typically at 0 ° C); the mixture is heated to 80-130 ° C and maintained at this temperature for 0.5-2 hours. Processing TiCl ₄ may be carried out one or more times. An internal electron donor may be added during the treatment with TiCl ₄ , and treatment with the electron donor compound may be repeated one or more times. Typically, a succinate of formula (I) is used in a molar ratio, with respect to MgCl ₂ , of from 0.01 to 1, preferably from 0.05 to 0.5. The preparation of spherical catalyst components is described, for example, in European Patent Application EP-A-395083 and International Patent Application WO98 / 44009. The solid catalyst components obtained in accordance with the above method show a surface area (BET method), typically between 20 and 500 m ² / g, and preferably between 50 and 400 m ² / g, and total porosity ( BET method) higher than 0.2 cm ³ / g, preferably between 0.2 and 0.6 cm ³ / g. The porosity (Hg method) associated with pores with a radius of up to 10,000Ǻ is typically in the range of 0.3 to 1.5 cm ³ / g, preferably 0.45 to 1 cm ³ / g.

The organic aluminum compound is preferably alkyl-Al selected from trialkylaluminum compounds, such as, for example, triethylaluminum, triisobutylaluminum, tri-n-butylaluminum, tri-n-hexylaluminum, tri-n-octylaluminum. It is also possible to use mixtures of trialkylaluminum with alkylaluminum halides, alkylaluminum hydrides or alkylaluminum sesquichlorides such as AlEt ₂ Cl and Al ₂ Et ₃ Cl ₃ .

Preferred external electron donor compounds include silicon compounds, esters such as ethyl 4-ethoxybenzoate, heterocyclic compounds, and in particular 2,2,6,6-tetramethylpiperidine, and ketones. Another class of preferred external electron donor compounds is silicon compounds of the formula R _a ⁵ R _b ⁶ Si (OR ⁷ ) _c , where a and b are integers from 0 to 2, c is an integer from 1 to 3, and the sum (a + b + c) is 4; R ⁵ , R ⁶ and R ⁷ are alkyl, cycloalkyl or aryl radicals with 1-18 carbon atoms, optionally containing heteroatoms. Particularly preferred are methylcyclohexyl dimethoxysilane, diphenyldimethoxysilane, methyl tert-butyldimethoxysilane, dicyclopentyldimethoxysilane, 2-ethylpiperidinyl-2-tert-butyldimethoxysilane and 1,1,1, trifluoropropyl-2-ethylpiperidinyl-dimethyl-dimethyl-dimethyl-dimethyl-dimethyl-dimethyl-dimethyl-dimethyl-dimethyl-dimethyl-dimethyl-dimethyl-dimethyl-dimethyl-dimethyl-dimethyldimethyl-dimethyl dimethoxysilane. The external electron donor compound is used in such quantity to obtain a molar ratio between the organic aluminum compound and said electron donor compound from 0.1 to 500.

The propylene polymers of the present invention may further comprise at least one nucleating agent. Preferably, the propylene polymers contain up to 2500 ppm, more preferably from 500 to 2000 ppm, of at least one nucleating agent.

At least one nucleating agent may be selected from inorganic additives such as talc, silicon oxide or kaolin, salts of monocarboxylic or polycarboxylic acids, for example, sodium benzoate or aluminum tert-butyl benzoate, dibenzylidene sorbitol or its C ₁ -C ₈ -alkyl substituted derivatives, such as methyldibenzylidene sorbitol, ethyldibenzylidene sorbitol or dimethyldibenzylidene sorbitol, or salts of phosphoric acid diesters, for example sodium or lithium 2,2'-methylenebis (4,6, -di-tert-butylphenyl) phosphate. Particularly preferred nucleating agents are 3,4-dimethyldibenzylidene sorbitol; aluminum hydroxy bis [2,2'-methylene bis (4,6-di-tert-butylphenyl) phosphate]; sodium or lithium 2,2'-methylene bis (4,6-ditretbutylphenyl) phosphate and the disodium salt of (1R, 2R, 3R, 4S) bicyclo [2.2.1] heptane-2,3-dicarboxylic acid. At least one nucleating agent can be added to the propylene polymer using known methods, such as melt mixing at least one nucleating agent and a propylene polymer under shear conditions in a conventional extruder.

The propylene polymers of the present invention, optionally containing a nucleating agent, preferably have a crystallization temperature Tc (measured by DSC) equal to or greater than 110 ° C, more preferably in the range of 110 ° C to 120 ° C, particularly preferably 112 ° to 117 ° C, and / or the melting temperature Tm (measured by DSC) is higher than 152 ° C, preferably a temperature in the range of 152 ° to 162 ° C.

The propylene polymers of the present invention have been found to be particularly suitable for the production of blow molded molded products.

An additional objective of the present invention, for this reason, is to provide a method for producing molded articles, extruded by blow molding, comprising the use of propylene polymers having a total content of units obtained from at least one linear or branched alpha-olefin having from 2 to 8 carbon atoms other than propylene in the range from 4.5 to 6.0 wt.%, Preferably from 4.7 to 5.5 wt.%, More preferably from 4.8 to 5.2 wt. %, and melting temperature Tm (measured using DSC for "polymer from the reactor"), ranging from 148 ° to 160 ° C, preferably from 150 ° to 158 ° C, more preferably from 153 ° C to 156 ° C.

In blow molding methods, a hollow cylinder (preform) is extruded from molten plastic material and clamped into a mold. Then the molten billet expands under air pressure, cools and is released. Burrs are an unavoidable by-product of the blown extrusion process, and a chipping tool is needed to remove burrs from blow molded products. For this reason, the cooling step is a factor limiting the speed of the process, and the ability of the molten material to cool is the most important in determining the minimum cycle time. It has been found that by using the propylene polymers of the present invention for blown extrusion molding processes, the cycle time can be significantly reduced compared to the same methods using conventional polypropylene.

It was unexpectedly found that a propylene polymer having a total comonomer content contained in the preferred range of 4.7 to 5.5 wt.% (Relative to the propylene polymer) additionally obtains a particularly advantageous balance of impact resistance / hardness, Izod impact resistance values at 0 ° C (measured in accordance with ISO 180 / 1A), which are higher than 10 kJ / m ² , preferably are in the range from 10 to 50 kJ / m ² , more preferably from 15 to 45 kJ / m ² .

In addition to nucleating agents, the propylene polymers of the present invention may additionally contain additives commonly used in the field of polyolefins, such as antioxidants, light stabilizers, antacids, colorants, fillers and process improvers, these additives are usually added to the propylene polymer in appropriate amounts in accordance with with methods well known in the art.

The properties mentioned in the description and examples are measured in accordance with the following methods. The examples are provided to illustrate and not to limit the present invention.

The molar ratio of the introduced gases : Determined by gas chromatography

Comonomer Content (C2) : By IR Spectroscopy

Melt Flow Rate (MFR): Determined in accordance with ISO 1133 (230 ° C, 2.16 kg)

Melting point and crystallization (Tm and Tc) : Determined by DSC in accordance with ISO 11357/3, with a temperature change of 20 ° C per minute.

Polydispersity Index (P.I.)

Determined at a temperature of 200 ° C by using a model of a rheometer with parallel plates RMS-800, manufactured by RHEOMETRICS (USA), operating at an oscillation frequency that increases from 0.1 rad / sec to 100 rad / sec. From the module at the intersection point, P.I. using the equation:

PI = 10 ⁵ / Gc,

where Gc is the modulus at the intersection, which is defined as the value (expressed in Pa) at which G '= G ", where G' is the dynamic modulus of elasticity and G" is the loss modulus.

Xylene Soluble Fraction (XS)

2.5 g of the polymer and 250 ml of o-xylene are introduced into a glass flask equipped with a refrigerator and a magnetic stirrer. The temperature is raised in 30 minutes to the boiling point of the solvent. The solution thus obtained was then heated under reflux and stirred for an additional 30 minutes. Then the closed flask is kept for 30 minutes in an ice bath, as well as in a thermostatic water bath at 25 ° C for 30 minutes. The solid product thus obtained is filtered on quick filter paper, and 100 ml of the filtered liquid is poured into a pre-weighed aluminum container, which is heated on a heated table in a stream of nitrogen to remove the solvent by evaporation. Then the container is kept in an oven at 80 ° C in vacuo until a constant weight is obtained. The residue was weighed to determine the percentage of xylene soluble polymer.

Bending Modulus (MEF) : Determined in accordance with ISO 178

Impact resistance Izod : Determined according to ISO 180 / 1A at 23 ° and 0 ° C

The transition temperature between the viscous and brittle state (DBTT): In accordance with this method, the biaxial impact resistance is determined by impact with an automatic, computerized hammer hammer. Round samples for research are obtained by cutting with a circular hand punch (diameter 38 mm) dies obtained as described below. Round test specimens were conditioned for at least 12 hours at 23 ° C and 50 RH (relative humidity), and then placed in a thermostatic bath at the test temperature for 1 hour. The time-dependence of the force is detected during the impact of the hammer (5.3 kg, hemispherical punch with a diameter of ½ inch) with a round sample resting on an annular support. The device used is CEAST 6758/000 type model No. 2. DBTT is the temperature at which 50% of the samples undergo brittle fracture when they are subjected to the impact study discussed above. Dies for measuring DBTT having dimensions of 127 × 127 × 1.5 mm, receive in accordance with the following method. The injection press is a Negri Bossi ™ type (NB 90) with a compression force of 90 tons. The form is a rectangular die (127 × 127 × 1.5 mm). The main parameters of the method are given below:

Back pressure bar twenty Injection time sec 3 Maximum injection pressure MPa fourteen Hydraulic injection pressure MPa 6-3 First hydraulic holding pressure MPa 4 ± 2 First aging time sec 3 Second holding hydraulic pressure MPa 3 ± 2 Second aging time sec 7 Cooling time sec twenty Mold temperature ° C 60 Melt temperature ° C 220-280

Matte (per 1 mm plate)

According to the present method, 5 × 5 cm samples are cut molded plates of 1 mm thickness, and the haze value is measured using a Gardner photometric device connected to a UX-10 nephelometer or an equivalent instrument having a G.E. light source. 1209 with filter "C". Reference samples with known haze are used to calibrate the instrument. The plates to be examined are prepared in the following ways. The plates 75 × 75 × 1 mm are formed using the GBF Plastiniector G235 / 90 Injection Molding Machine, 90 tons, under the following processing conditions:

Screw rotation speed rpm 120 Back pressure bar 10 Melting temperature ° C 260 Injection time sec 5 Switching to holding pressure bar fifty First stage holding pressure bar thirty Second stage pressure bar twenty Pressure Hold Profile:
-1 stage sec 5  -2 stage sec 10 Cooling time sec twenty Water temperature to cool the mold ° C 40

Maximum load: Instron dynamometer equipped with a balance with an accuracy of 0.2 g and a micrometer with an accuracy of 0.01 mm are used for research. After at least 10 hours of conditioning at 23 ° ± 1 ° C and 50% relative humidity, the bottle is placed between two dynamometer plates and compressed at a plate speed of 5 cm / min. The voltage at the collapse of the bottle is recorded, and its value is expressed in N. The value of the maximum load is the average value obtained from measurements repeated on 10 bottles.

Polymerization Equipment

For examples 1-3, in accordance with the present invention, a gas phase polymerization reactor is used comprising two interconnected polymerization zones, a vertical column and a downflow pipe, as described in International Patent Application WO 00/02929, to produce propylene polymers (A) . The indicated amounts of ethylene and a molecular weight regulator, that is, hydrogen, are introduced exclusively into the first polymerization zone (vertical column). The gas composition in the two polymerization zones differs due to the transition of the propylene stream.

Examples 1-3

A solid catalyst used to produce propylene polymers is prepared according to Example 5, lines 48-55 of European patent EP 728769. Triethylaluminium (TEAL) is used as cocatalyst and dicyclopentyl dimethoxysilane as an external electron donor. Propylene polymers are prepared in one polymerization step by introducing monomers and a catalyst system into the polymerization equipment described above. The polymer powders are subjected to steam treatment to remove unreacted monomers, dried and subjected to the analyzes shown in Table 1 together with the polymerization conditions.

Table 2 shows the characterization data measured on the compositions obtained by mixing the polymer powders of Examples 1-3 with 900 ppm. ADK-NA21 (aluminum-hydroxybis [2,2'-methylene-bis (4,6-di-tert-butylphenyl) phosphate] supplied by Adeka Palmarole) in a Werner 53 extruder. In addition, from these compositions are obtained by technology blow molding, bottles (35 g) that are tested for impact properties (4 ° C) and maximum load properties.

Table 1 Project 1 Project 2 Project 3 TEAL / external electron donor wt./wt. 3.8 3.9 3.0 TEAL / catalyst wt./wt. 5,0 5,0 5,0 Temperature ° C 75 70 75 Pressure bar in the sensor 24 22 24 Relative mass content vertical column wt.% 38 35 34 downflow pipe wt.% 62 65 66 C ₃ ^- , vertical column mol% 66 70.5 / C ₂ ^- , vertical column mol% 8 4.9 / H ₂ / C ₃ ^- , vertical column mol / mol / 0,030 0.006 C ₂ ^- / (C ₂ ^- + C ₃ ^- ) mol / mol / 0,065 0,050 Analysis for polymer powder Mfr g / 10 min 2.0 2,4 0.9 C ₂ , general content wt.% 4.7 5 4.8 XS wt.% 12.8 11.5 12.1 Polydispersity index 4.4 4.8 4.2 Tm ° C 151.8 151.5 149.0 Tc ° C 101 97.4 99.8

Comparative Example 1

In the same Table 2, characterization data for a conventional propylene / ethylene copolymer suitable for blown extrusion molding, available on the market and manufactured by Basell in a conventional loop reactor, are given. The copolymer is melt blended in a Werner 53 extruder with 1800 ppm. Millad 3988. The MFR for the copolymer is 1.5 g / 10 min.

Reference Example 2

In accordance with the description of European patent EP1206499, the propylene polymer composition is prepared using the same solid catalyst as in Example 2.

Triethylaluminium (TEAL) is used as a cocatalyst. The polymerization reaction is carried out, as described in the above example, by introducing monomers into the first liquid phase reactor operating at a temperature of 70 ° C, equipped with devices suitable for transferring growing polymers together with unreacted monomers and catalyst systems to a second gas phase reactor, where the polymerization reaction is completed at a temperature of 80 ° C by introducing an appropriate amount of fresh monomers. Hydrogen is used as a molecular weight regulator. The composition of the propylene polymer from the reactor has a melting point of 145.4 ° C and contains 86 wt.% Propylene-ethylene copolymer containing 3.0 wt.% Units derived from ethylene, and 14% by weight, propylene-ethylene copolymer containing 16, 3 wt.% Units derived from ethylene.

The polymer powder released from the second reactor is subjected to steam treatment to remove unreacted monomers, dried and melt mixed in a 1800 ppm twin-screw Berstorff extruder. Mi Had 3988 (1.3: 2,4-bis (3,4-dimethyldibenzylidene sorbitol). The composition has a MFR of 1.3 g / 10 min, a total fraction soluble in xylene of 12.6 wt.%. Characterization data are given in Table 2.

table 2 Project 1 Project 2 Project 3 Comp. pr.1 Comp. pr.2 TT ° C 154.5 153.8 152 143.2 149, 0 Tf ° C 116.3 116 112.7 104, 9 / Bending modulus MPa 870 830 890 840 790 Izod at 23 ° C kJ / m ² 60.3 54 59 35.0 N.B. Izod at 0 ° C kJ / m ² 34.6 37.3 28.6 6.0 4.0 DBTT ° C -5.4 -3.2 -4.6 10.0 -2.0 Dull % 16.6 14.9 15.4 10.0 11.0 Bump on the bottles (4 ° C) cm 126 121 144 62 Maximum load N 270 270 290 275 N.B. = does not break

Also, after nucleation, the propylene polymers of the present invention retain higher Tm and Tc compared to conventional propylene copolymers containing the same amount of comonomer. In addition, from Table 2 it is clear that the copolymers of the present invention show excellent impact properties, in particular at low temperatures, which in turn are reflected in blow molded products.

Claims (6)

1. The propylene polymer having a total content of units derived from ethylene, in the range from 4.5 to 6.0 wt.%, And a melting temperature Tm (measured using DSC on the polymer from the reactor), in the range from 148 to 160 ° C. 2. The propylene polymer according to claim 1, additionally containing up to 2500 ppm of at least one nucleating agent. 3. The propylene polymer according to any one of claims 1 and 2, having a total ethylene content in the range from 4.7 to 5.5 wt.%. 4. The gas-phase polymerization method for producing a propylene polymer according to any one of claims 1 to 3, carried out in at least two interconnected polymerization zones, comprises introducing propylene and ethylene into said polymerization zones in the presence of a highly stereospecific heterogeneous Ziegler-Natta catalyst system under the reaction conditions and collection of the polymer product from the indicated polymerization zones, in the specified method, the growing polymer particles flow up through one of the indicated polymerization zones (vertical column) under x fast liquefaction, leave the specified vertical column and enter a different polymerization zone (downward flow pipe), through which they flow down under the action of gravity, leave the specified downward flow pipe and re-enter the vertical column, thus establishing polymer circulation between a vertical column and a pipe with a downward flow, while creating means that are able to fully or partially prevent the flow of the gas mixture present in the vertical columns In the downcomer, and gas and / or liquid mixture having a composition different from that of the gas mixture present in a vertical column, is introduced into the downcomer, the method further characterized in that
the ratio of the introduced monomers C _x ^- / (C _x ^- + C ₃ ^- ) for the vertical column is in the range from 0.050 to 1,000 mol / mol, where C _x ^is ethylene as a comonomer to produce propylene polymers and C ₃ ^is propylene . 5. A method of obtaining molded products, extruded by blow molding, comprising the use of a propylene polymer according to any one of claims 1 to 3. 6. A blow molded product containing a propylene polymer according to any one of claims 1 to 3.