MXPA00006580A - Polyolefin composition having a high balance of stiffness and impact strength - Google Patents

Abstract

A polyolefin composition comprising (percentage by weight):(A) from 40 to 60%of a broad molecular weight distribution propylene polymer (component A) having a polydispersity index from 5 to 15 and melt flow rate of from 80 to 200 g/10 min (according to ASTM-D 1238, condition L);and (B) from 40 to 60%of a partially xylene-insoluble olefin polymer rubber (component B) containing at least 65%by weight of ethylene;the IVS/IVA ratio between the intrinsic viscosity (IVS) of the portion soluble in xylene of the polyolefin composition at room temperature and the intrinsic viscosity (IVA) of component (A) ranging from 2 to 2.5, both values on intrinsic viscosity being measured in tetrahydronaphthalene at 135°C. Said composition finds application in automotive field.

Description

COMPOSITION OF POLIOLEFINA THAT CONTAINS A HIGH BALANCE OF RIGIDITY AND IMPACT RESISTANCE DESCRIPTIVE MEMORY The present invention relates to an elastomeric thermoplastic polyolefin composition. In particular, the present invention relates to compositions containing a propylene polymer of broad molecular weight distribution. Due to its mechanical and physical properties, the polymer composition of the present invention finds application primarily in the automotive field (e.g., fenders and moldings). Said polyolefin composition has a good balance of mechanical properties, in particular improved equilibrium of flexural modulus and impact resistance of IZOD even at low temperatures (for example at -30 ° C). In addition to the above properties, the composition of the present invention is endowed with satisfactory optical properties. As required by the market, the composition shows low brightness values. An added advantage, which is shown by the composition of the present invention, is that it has a low coefficient of linear thermal expansion coefficient (CLTE). Said property imparts a higher dimensional stability to articles produced with the polyolefin composition of the present invention. Therefore, an object of the present invention is a polyolefin composition comprising (in percent by weight): (A) from 40 to 60%, preferably 40 to 55%, of a propylene polymer of broad weight distribution molecular (component A) having a polydispersity index of 5 to 15 and melt flow rate of 80 to 200 g / 10 min (in accordance with ASTM-D 1238, condition L); and (B) from 40 to 60%, preferably 45 to 60%, of an olefin polymer rubber partially soluble in xylene (component B) containing at least 65% by weight of ethylene; the IVS / IVA ratio between the intrinsic viscosity (IVS) of the xylene-soluble portion of the polyolefin composition at room temperature and the intrinsic viscosity (IVA) of the component (A) is on the scale of 2 to 2.5, preferably of 2.1 to 2.4, both values of intrinsic viscosity being measured in tetrahydronaphthalene at 135 ° C. The method for measuring the xylene-soluble content and the polydispersity index is described hereinafter. The ambient temperature means a temperature of about 25 ° C in the present application. The polyolefin composition of the present invention may further contain a mineral filler. When present, it is contained in an amount of 0.5 to 3 parts by weight with respect to the sum of the components (A) and (B).

The composition of the present invention typically has a melt flow rate of 5 to 20 g / 10 min. In addition, typically, it has a flexural modulus of 650 to 1000 MPa, preferably 700 to 1000 MPa. Preferably the coefficient of linear thermal expansion is up to 8 ° C x 10"5, more preferably 5 to 8, the flexibility of IZOD slotted at -30 ° C is typically 15 KJ / m2 or higher, preferably 18 KJ / m2 Typically, gloss values are lower than 50% The methods for measuring the mentioned properties are described below Component (A) is a crystalline propylene homopolymer or a copolymer of propylene with ethylene or C4 α-olefin -C-? Or a mixture thereof Ethylene is the preferred comonomer The comonomer content is on the scale preferably 0.5 to 1.5% by weight, more preferably 0.5 to 1% by weight. xylene at 25 ° C of component (A) is typically greater than 90%, preferably equal to or greater than 94% Preferably, component (A) has a melt flow rate of 80 to 150 g / 10 min. Component (A) approximately has a distribution of p that molecular PMp / PMn, (PMP = weight average molecular weight and PMn = number average molecular weight, both measured by gel permeation chromatography) from 8 to 30, more preferable from 8.5 to 25. The olefin polymer rubber of component (B) used in the polyolefin composition of the present invention may be a poly (C3-C10 ethylene-α-olefin) or poly (ethylene-co-propylene-co-α-olefin of C 4 -C 0) having an ethylene content preferably of 65 to 80% by weight. The latter contains from 0.5 to 10% by weight of an α-olefin of C4-C? O. The olefin polymer rubber may optionally also contain a diene, the content of which is preferably 1 to 10% by weight, more preferably 1 to 5% by weight. The olefin polymer rubber of component (B) is partially soluble in xylene at room temperature. The content not soluble in xylene is about 25-35% by weight, preferably 27-33% by weight. The C3-C10 α-olefins useful in the preparation of the component (B) described above include propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene and 1-ketene. Propylene and 1-butene are particularly preferred. The mineral filler, when present, is preferably selected from talc, calcium carbonate, silica, conventional clays, wollastonite, diatomaceous earth, titanium oxide and zeolites. Preferably, the mineral filler is talc. In addition to the mineral fillers discussed above, the polyolefin composition of the present invention may contain conventional additives, for example, stabilizers, pigments, other fillers and reinforcing agents, for example carbon black and glass spheres and fibers.

The polyolefin composition of the present invention can be prepared by means of a physical mixture or chemical mixture. Preferably, the composition of the present invention is prepared directly in polymerization by sequential polymerization procedures in a series of reactors based on the use of particular stereospecific Ziegler-Natta catalysts, producing by polymerization a mixture of component (A) and component ( B). Subsequently, the mineral filler is optionally added by mixing, or in the final pelletizing section of the industrial polymerization plant. The polymerization process is carried out in at least three consecutive stages, in the presence of particular stereospecific Ziegler-Natta catalysts, supported on a magnesium halide in active form. In particular, the propylene polymer of broad molecular weight distribution of the component (A) described above can be prepared by sequential polymerization in at least two stages and in the olefin polymer rubber in the other steps. Alternatively, the polyolefin composition of the present invention can be physically mixed or mixed in any conventional mixing apparatus, such as an extruder or a Banbury mixer, by mixing components (A) and (B) and optionally the components additional The components (B) and (A) are mixed in the molten or softened state.

As mentioned above, the polymerization step can be carried out in at least three sequential steps, in which the components (A) and (B) are prepared in separate steps separately, operating in each step in the presence of the polymer formed and the catalyst used in the immediately preceding step. The catalyst is added only in the first step, however its activity is such that it is still active for all subsequent steps. The order in which components (A) and (B) are prepared is not critical. However, it is preferred to produce the component (B) after producing the component (A). The catalyst used to prepare component (A) is preferably characterized in that it is capable of producing propylene polymers having a fraction not soluble in xylene at 25 ° C greater than or equal to 90% by weight, preferably larger than or equal to to 94%. Moreover, it has a sensitivity to molecular weight regulators high enough to produce propylene homopolymers having a molten material flow rate in the range of 1 to 20 g / 10 min and larger than 200 g / 10 min. The methods for preparing the propylene polymer of broad molecular weight distribution of the component (A) of the present invention are described in the European patent application 573 862. The catalyst mentioned above is used in all steps of the polymerization process of the present invention to directly produce the sum of components (A) and (B).

Catalysts having the characteristics mentioned above are well known in the patent literature; the catalysts described in the US patent are particularly advantageous. 4,399,054 and European patents 45977 and 395083. The polymerization process can be carried out continuously or in batches, according to known techniques and operating in liquid phase, in the presence or absence of inert diluent, or in gas phase or in mixed phases of liquid-gas. It is preferable to operate in the gas phase. The time and the reaction temperature are not critical; however, the temperature is typically in the range of 20 to 100 ° C. Preferably, the reaction temperature is generally 40 to 65 ° C for the polymerization of the component (B). Molecular weight regulation is carried out using regulators known as hydrogen. An essential component of the Ziegler-Natta catalyst used in the polymerization process of the present invention is a solid catalyst component comprising a titanium compound having at least one titanium-halogen bond, and an electron donor compound, both supported on a magnesium halide in active form. Another essential component (co-catalyst) is an organoaluminum compound, such as an alkylaluminum compound. An external donor is also added optionally.

The solid catalyst components used in said catalyst comprise, as electron donors (internal donors), compounds selected from the group consisting of ethers, ketones, lactones, compounds containing N, P and / or S atoms, and esters of mono- and dicarboxylic. Particularly suitable electron donor compounds are esters of italic acid, such as diisobutyl phthalate, dioctyl, diphenyl and benzylbutyl phthalate. Other particularly suitable electron donors are 1,3-diethers of the formula: wherein R1 and R11 are identical or different and are C-t-d-alkyl, C3-C18 cycloalkyl or C7-C8 aryl radicals; R1"and R? V are identical or different and are C? .C alkyl radicals, or are the 1,3-diethers in which the carbon atom in position 2 belongs to a cyclic or polycyclic structure formed of up to 5, 6 or 7 carbon atoms and contain two or three unsaturations Ethers of this type are described in published European patent applications 361493 and 728769. Representative examples of said dieters are as follows: 2-methyl-2-isopropyl -1, 3-dimethoxypropane, 2,2-diisobutyl-1,3-dimethoxypropane, 2-isopropyl-2-cyclopentyl-1,3-dimethoxypropane, 2-isopropyl-2-isoamyl-1,3-dimethoxypropane and 9.9 bis (methoxymethyl) fluorene The preparation of the aforementioned catalyst components is carried out according to various methods, for example, a MgCl 2 * nROH adduct (in particular in the form of spherical particles) in which n is generally 1. to 3 and ROH is ethanol, butanol or isobutanol, it is reacted with an excess of TiCl that It has the electron donor compound. The reaction temperature is generally 80 to 120 ° C. The solid is then isolated and reacted once again with TiCl4, in the presence or absence of the electron donor compound, after which it is separated and washed with aliquots of a hydrocarbon until all the chlorine ions have disappeared. In the solid catalyst component the titanium compound, expressed as Ti, is generally present in an amount of 0.5 to 10% by weight. The amount of electron donor compound that remains fixed on the solid catalyst component is generally 5 to 20 mole% with respect to the magnesium dihalide. The titanium compounds, which can be used for the preparation of the catalyst component, are the halides and the titanium halide alcoholates. Titanium tetrachloride is the preferred compound. The reactions described above result in the formation of a magnesium halide in active form. Other reactions are known in the literature, which cause the formation of magnesium halide in active form starting from magnesium compounds other than halides, such as magnesium carboxylates. The Al-alkyl compounds used as co-catalysts comprise the Al-trialkyls, such as Al-triethyl, Al-triisobutyl, Al-tri-n-butyl, and linear or cyclic Al-alkyl compounds containing two or more Al-linked atoms. to another by means of atoms O or N, or groups SO4 or SO3. The Al-alkyl compound is generally used in such an amount that the Al / Ti ratio is from 1 to 1000. Electron donor compounds that can be used as external donors include esters of aromatic acids such as alkylbenzoates and in particular silicon compounds containing at least one Si-OR bond, wherein R is a hydrocarbon radical. Useful examples of silicon compounds are (tert-butyl) 2 Si (OCH) 2, (cyclohexyl) (methyl) Si (OCH3.-2, (phenyl) 2 Si (OCH3) 2 and (cyciopentyl) 2 Si (OCH3) 2. The 1,3-diethers having the above-described formulas can also be advantageously used.If the internal donor is one of these dieters, the external donors can be omitted.The catalysts can be pre-contacted with small amounts of olefins (prepolymerization), thus improving, both the performance of the catalyst and the morphology of the polymers. The prepolymerization is carried out by keeping the catalyst in suspension in a hydrocarbon solvent (for example, hexane or heptane) and polymerizing at an ambient temperature at 60 ° C for a sufficient time to produce polymer amounts of 0.5 to 3 times the weight of the solid catalyst component. It can also be carried out in liquid propylene, at the temperature conditions indicated above, producing amounts of polymer that can reach up to 1000 g per g of catalyst component. As mentioned above, the polyolefin composition of the present invention can also be obtained by mixing. The mixing is done using known techniques starting from pellets or powders or particles of the polymers obtained from the polymerization processes, which are preferably pre-mixed with the mineral filler in the solid state (for example, with a Banbury, Henshel or Lodige mixer). ) and then extruded. As mentioned above, the polymer composition of the present invention is suitable for preparing defenses and other vehicle parts, such as sidebands. Hence, the polymer composition is subjected to the conventional techniques used to prepare said articles. The following analytical methods are used to characterize the propylene polymer of the component (A), the rubber copolymer of the component (B) and the composition obtained therefrom.

Melt flow rate: determined in accordance with ASTM-D 1238, condition L.

Intrinsic viscosity i? L: determined in tetrahydronaphthalene a 135 ° C.

Ethylene: determined according to I.R. spectroscopy Soluble and insoluble in xylene: 2.5 g of polymer are dissolved in 250 ml of xylene at 135 ° C under agitation. After 20 minutes the solution is allowed to cool to 25 ° C, still under stirring, and then left to stand for 30 minutes. The precipitate is filtered with filter paper, the solution evaporated in nitrogen flow, and the residue dried under vacuum at 80 ° C until a constant weight is reached. In this way, the percentage by weight of soluble and insoluble polymer in xylene at room temperature (25 ° C) is calculated. polydispersity index (P.I.); Measurement of the molecular weight distribution in the polymer. To determine the PI value, the module separation at a lower module value, for example 500 Pa, is determined at a temperature of 200 ° C using a parallel plate rheometer model RMS-800 marketed by Rheometrics (USA), operating at an oscillation frequency that increases from 0.01 rad / second to 100 rad / second. From the module separation value, the value P.l. it can be derived using the following equation: P.l. = 54.6 (module separation) "1 76 in which the module separation (MS) is defined as: MS = (frequency a G '= 500 Pa) / (frequency a G" = 500 Pa) in which G' is the storage module and G "is the lower module.

Bending module: determined in accordance with ASTM-D 790.

CLTE: this test method is based on the methods ASTM D 696 and E831-86. Before the CLTE measurement the sample is conditioned in the TMA (thermomechanical analysis) apparatus at 120 ° C for 10 minutes in order to erase the induced stresses in the sample (3.5 mm thick and 10 mm long) by injection molding . After that, the expansion curve is measured on the temperature scale from 0 to 130 ° C at scanning speed of 3 ° C / min under the probe, the load of which is 1 mN (flat probe of 3.66 mm in diameter). The CLTE measurement is carried out longitudinally with respect to the polymer injection line. CLTE is determined as alpha =? L _ / (L ° x? T) on the temperature scale of 23-80 ° C. ? L: variation in length on the temperature scale from 23 to 80 ° C.

? T: 80-23 = 57 ° C. L °: initial sample length.

IZOD impact test slotted at -30 ° C: determined in accordance with ASTM-D 256 / A.

Gloss: determined according to ASTM-D 2457. The following examples are given in order to illustrate and not to limit the present invention.

E J EMPLOS 1-2 AND COMPARATIVE EXAMPLES 1C-2C Preparation of the solid catalyst component The MgC ^ / alcohol adducts in spherical form are prepared following the method described in Example 2 of the US patent. No. 2,399,054 but running at 3,000 RPM instead of 10,000 RPM. The adduct is partially dealcoholated by heating at temperatures that increase from 30 to 180 ° C operating in nitrogen stream. Into a 1-liter flask equipped with a condenser and mechanical stirrer, under a stream of nitrogen, 625 ml of TiCl4 are introduced. At 0 ° C while stirring, 25 g of partially dealcoholated adduct are added. This is then heated to 100 ° C in 1 hour; when the temperature reaches 40 ° C, diisobutyl phthalate (DIBF) is added in a Mg / DIBF = 8 molar ratio. The temperature is maintained at 100 ° C for 2 hours. Then let it decant and then the hot liquid is siphoned. 550 ml of TiCl4 are added and heated at 120 ° C for 1 hour. Finally, it is allowed to settle and the liquid is siphoned while it is hot; the residual solid is washed 6 times with 200 ml aliquots of anhydrous hexane at 60 ° C and 3 times at room temperature. The solid is then dried under vacuum.

Polymerization Polymerization is carried out continuously in a series of reactors equipped with devices to transfer the product from one reactor to the next. In the gas phase, hydrogen propane and monomers are continuously analyzed and fed in order to keep the desired concentrations constant. In the polymerization operation, a mixture of a triethylaluminum activator (TEAL) and dicyclopentyldimethoxysilane (DCPMS) as the electron donor component is contacted with the solid catalyst component such that the weight ratio of TEAL / Cat is 5, a reactor at 30 ° C for 9 minutes. The TEAL compound and electron donor is in such quantities that the weight ratio of TEAUDCPMS is 15.

The catalyst is then transferred to a reactor containing an excess of liquid propylene and plymerized for 33 minutes at 25 ° C. The plymer is then transferred to the first gas phase reactor where the propylene homopolymerization occurs to obtain propylene homopolymers with low MFR. The product obtained in this way is then transferred to the second reactor, where the propylene is homopolymerized to obtain homopolymers with high MFR. Finally, the product of the second reactor is transferred to the third reactor, where the ethylene is copolymerized with propylene to obtain the component (B). The polymerization conditions used in each reactor are shown in Table I and the properties of the products obtained in this way are shown in Table II.

TABLE I TABLE II

Claims (8)

NOVELTY OF THE INVENTION CLAIMS

1. - A polyolefin composition comprising (percentage by weight): (A) from 40 to 60% of a propylene polymer of broad molecular weight distribution (component A) having a polydispersity index of 5 to 15 and flow rate of molten material from 80 to 200 g / 10 min (in accordance with ASTM-D 1238, condition L); and (B) from 40 to 60% of an olefin polymer rubber partially insoluble in xylene (component B) containing at least 65% by weight of ethylene; the IVS / IVA ratio between the intrinsic viscosity (IVS) of the xylene-soluble portion of the polyolefin composition at room temperature and the intrinsic viscosity (IVA) of the component (A) on the scale of 2 to 2.5, preferably of 2.1 to 2.4, both values on intrinsic viscosity being measured in tetrahydronaphthalene at 135 ° C.

2. The polyolefin composition according to claim 1 further characterized in that it contains from 0.5 to 3 parts by weight with respect to the sum of the components (A) and (B) of mineral fillers.

3. The polyolefin composition according to claim 2, further characterized in that it has a melt flow rate of 5 to 20 g / 10 min.

4. - The polyolefin composition according to claim 2 further characterized in that the component (A) has a molten material flow rate of 80 to 150 g / 10 min.

5. The polyolefin composition according to claim 2 further characterized in that the component (B) is a poly (ethylene-co-propylene).

6. A process for preparing the polyolefin composition according to claim 1 further characterized in that the monomers are polymerized in the presence of stereospecific catalysts supported on active magnesium halide in active form in at least three sequential steps, in which the components (A) and (B) are prepared in separate subsequent steps, operating in each step in the presence of the polymer formed and the catalyst used in the immediately preceding step.

7. Articles produced by the polyolefin composition according to claim 1.

8. Defenses produced by the polyolefin composition according to claim 1.