Molded article comprising propylene homopolymer

Abstract

A molded article comprising a propylene homopolymer, optionally containing up to 1.0% by weight of ethylene derived units, characterized in that: two melting points are present-the higher melting point ranges from 155 DEG C to 170 DEG C; -a fraction soluble in xylene at 25 DEG C is comprised between 6.0 wt% and 2.0 wt%; -the range of the isotactic five-unit group (mmmm%) is from 96.5 mol% to 90.0 mol%. -the intrinsic viscosity (IV) measured in tetrahydronaphthalene at 135 DEG C ranges from 5.5 dl / g to 12.0 dl / g-the melt strength is higher than 0.70 N.

Description

Technical Field

[0001] The present disclosure relates to molded articles, preferably compression molded articles comprising polypropylene homopolymer having high molecular weight and high abrasion resistance. Background Art

[0002] Propylene homopolymers are widely used in the field of molding processes such as injection molding or compression molding.

[0003] For many applications, wear resistance is an important feature of articles made of polymeric materials, and scratch and / or mar resistance is an important feature of articles made of polymeric materials, especially for polypropylene. For example, in the automotive industry, durable plastic products are required as external and internal parts, especially if they are part of moving parts (such as gears).

[0004] Therefore, there is a need to develop a propylene homopolymer for molded objects having enhanced abrasion resistance. Summary of the invention

[0005] The present disclosure relates to a molded article comprising a propylene homopolymer optionally containing up to 1.0 wt.% of ethylene-derived units, characterized in that:

[0006] - the presence of two melting points in the DSC thermogram measured according to ISO 11357-3 at a heating and cooling rate of 20°C / min;

[0007] - the higher melting point ranges from 155°C to 170°C measured according to ISO 11357-3 at a heating and cooling rate of 20°C / min;

[0008] - the fraction soluble in xylene at 25° C., measured according to ISO 16 152-2005, is comprised between 2.0% and 6.0% by weight;

[0009] - As reported in the Examples section, with C 13 The isotactic pentad mmmm% measured by NMR ranged from 90.0 mol% to 96.5 mol%;

[0010] - an intrinsic viscosity (IV) measured in tetralin at 135° C. ranging from 5.5 dl / g to 12.0 dl / g;

[0011] - at 250°C and at an applied speed equal to 6 mm / s 2 The melt strength measured according to ISO 16790-2005 under acceleration conditions is higher than 0.070N. DETAILED DESCRIPTION

[0012] The present disclosure relates to a molded article comprising a propylene homopolymer optionally containing up to 1.0 wt. % ethylene, preferably up to 0.6 wt. % ethylene-derived units, characterized in that:

[0013] - the presence of two melting points in the DSC thermogram measured according to ISO 11357-3 at a heating and cooling rate of 20°C / min; preferably the lower melting point is in the range of 135°C to 150°C;

[0014] - the higher melting point is in the range of 155°C to 170°C; preferably 157°C to 168°C, measured according to ISO 11357-3 at a heating and cooling rate of 20°C / min;

[0015] - the fraction soluble in xylene at 25° C., measured according to ISO 16 152-2005, is comprised between 2.0 and 6.0% by weight; preferably comprised between 2.5 and 5.0% by weight; more preferably comprised between 2.8 and 4.0% by weight;

[0016] - As reported in the Examples section, with C 13 The isotactic pentad mmmm% measured by NMR ranges from 90.0 mol% to 96.5 mol%; preferably from 93.0 mol% to 96.0 mol%; more preferably from 93.5 mol% to 95.5 mol%;

[0017] - an intrinsic viscosity (IV) measured in tetralin at 135° C. ranging from 5.5 dl / g to 12.0 dl / g; preferably from 7.0 dl / g to 11.0 dl / g; more preferably from 8.0 dl / g to 10.0 dl / g;

[0018] - at 250°C and at an applied speed equal to 6 mm / s 2 The melt strength measured according to ISO 16790-2005 under an acceleration of 1000 N is higher than 0.070 N; preferably higher than 0.080 N; more preferably higher than 0.090 N.

[0019] Preferably, the propylene homopolymers of the present disclosure are not nucleated.

[0020] Preferably, the homopolymers of the present disclosure exhibit melt strength values ​​below 0.29N.

[0021] Preferably, the homopolymers of the present disclosure exhibit a polydispersity index PI measured according to ISO 6721-10 comprised between 4.5 and 7.5; more preferably between 5.0 and 7.2; more preferably between 5.5 and 6.5.

[0022] Preferably, the homopolymers of the present disclosure exhibit a tensile modulus ranging from 2100 MPa to 1100 MPa; preferably from 1800 MPa to 1200 MPa.

[0023] Preferably, the homopolymers of the present disclosure exhibit a relative humidity of 4.0 kJ / m at 23°C. 2 Up to 11.0 kJ / m 2 ; preferably 5.5 kJ / m 2 Up to 9.0kJ / m 2 Charpy impact test.

[0024] The polypropylene homopolymers of the present disclosure are characterized by having high melt strength and high molecular weight. Therefore, the homopolymers of the present disclosure preferably show low wear resistance values ​​measured according to ISO 15527:2007. The average wear index value measured according to ISO 15527:2007 on compression molded substrates may be lower than 360; preferably lower than 355. The low wear index value makes the molded articles of the present disclosure particularly suitable for the production of automotive articles, especially articles subjected to movement.

[0025] The propylene homopolymer disclosed herein can be prepared by a method comprising polymerizing propylene optionally with ethylene in the presence of a Ziegler-Natta catalyst. An essential component of the catalyst is a solid catalyst component comprising a titanium compound having at least one titanium-halogen bond and an electron donor compound, both of which are supported on a magnesium halide in an active form. Another essential component (cocatalyst) is an organoaluminum compound, such as an alkylaluminum compound. An external donor is optionally added.

[0026] Catalysts having the above characteristics are well known in the patent literature; particularly advantageous are the catalysts described in US Pat. No. 4,399,054 and European Patent No. 45977. Other examples can be found in US Pat. No. 4,472,524.

[0027] The solid catalyst component used in the catalyst comprises as an electron donor (internal donor) a compound selected from the group consisting of ethers, ketones, lactones, compounds containing N, P and / or S atoms, and esters of mono- and dicarboxylic acids.

[0028] Particularly suitable electron donor compounds are esters of succinic acid (succinates). Preferably, the succinates present in the solid catalyst component are selected from succinates of the following formula (I):

[0029]

[0030] wherein the free radicals R1 and R2 are identical or different from each other and are C1-C20 straight or branched alkyl, alkenyl, cycloalkyl, aryl, arylalkyl or alkylaryl groups, optionally containing heteroatoms; and the free radicals R3 and R4 are identical or different from each other and are C1-C20 alkyl, C3-C20 cycloalkyl, C5-C20 aryl, arylalkyl or alkylaryl groups, provided that at least one of them is a branched alkyl group; the compound is a (S, R) or (R, S) type stereoisomer relative to the two asymmetric carbon atoms identified in the structure of formula (I)

[0031] R1 and R2 are preferably C1-C8 alkyl, cycloalkyl, aryl, arylalkyl and alkaryl. Particularly preferred are compounds in which R1 and R2 are selected from primary alkyl, especially branched primary alkyl. Examples of suitable R1 and R2 groups are methyl, ethyl, n-propyl, n-butyl, isobutyl, neopentyl, 2-ethylhexyl. Particularly preferred are ethyl, isobutyl and neopentyl.

[0032] Particularly preferred are compounds in which the R3 and / or R4 radicals are secondary alkyl radicals such as isopropyl, sec-butyl, 2-pentyl, 3-pentyl or cycloalkyl radicals such as cyclohexyl, cyclopentyl, cyclohexylmethyl.

[0033] Examples of such compounds are diethyl 2,3-bis(trimethylsilyl)succinate, diethyl 2,3-bis(2-ethylbutyl)succinate, diethyl 2,3-dibenzylsuccinate, diethyl 2,3-diisopropylsuccinate, diisobutyl 2,3-diisopropylsuccinate, diethyl 2,3-bis(cyclohexylmethyl)succinate, diethyl 2,3-diisobutylsuccinate, diethyl 2,3-dineopentylsuccinate, diethyl 2,3-dicyclopentylsuccinate, diethyl 2,3-dicyclohexylsuccinate in (S,R)(S,R) pure form or in the form of a mixture, optionally in racemic form.

[0034] Particularly suitable electron donor compounds are esters of phthalic acid and 1,3-diethers of the following formula:

[0035]

[0036] wherein RI and RII are identical or different and are C1-C18 alkyl, C3-C18 cycloalkyl or C7-C18 aryl radicals; RIII and RIV are identical or different and are C1-C4 alkyl radicals; or is a 1,3-diether, wherein the carbon atom at position 2 belongs to a cyclic or polycyclic structure consisting of 5, 6 or 7 carbon atoms or 5-n or 6-n' carbon atoms and n nitrogen atoms and n' heteroatoms selected from the group consisting of N, O, S and Si, respectively, wherein n is 1 or 2 and n' is 1, 2 or 3, said structure containing two or three degrees of unsaturation (cyclic polycyclic structure); alkyl radicals) and optionally condensed with other cyclic structures, or substituted by one or more substituents selected from the group consisting of: straight or branched alkyl radicals, cycloalkyl radicals, aryl, aralkyl, alkaryl radicals and halogens, or condensed with other cyclic structures and substituted by one or more of the above substituents, one or more of which may also be bonded to the condensed cyclic structure; a condensed cyclic structure of one or more of the above alkyl, cycloalkyl, aryl, aralkyl or alkaryl radicals and optionally containing one or more heteroatoms as substituents of carbon atoms or hydrogen atoms or both.

[0037] Ethers of this type are described in published European Patent Applications 361,493 and 728,769.

[0038] Representative examples of the diethers are 2-methyl-2-isopropyl-1,3-dimethoxypropane, 2,2-diisobutyl-1,3-dimethoxypropane, 2-isopropyl-2-cyclopentyl-1,3-dimethoxypropane, 2-isopropyl-2-isopentyl-1,3-dimethoxypropane, 9,9-bis(methoxymethyl)fluorene.

[0039] Other suitable electron donor compounds are phthalic acid esters, such as diisobutyl phthalate, dioctyl phthalate, diphenyl phthalate and benzyl butyl phthalate.

[0040] The preparation of the above-mentioned catalyst components is performed according to various methods.

[0041] For example, MgCl2.nROH adduct (especially in the form of spherical particles) (where n is generally from 1 to 3 and ROH is ethanol, butanol or isobutanol) is reacted with an excess of TiCl4 containing an electron donor compound. The reaction temperature is generally 80° C. to 120° C. The solid is then separated and reacted once more with TiCl4 in the presence or absence of an electron donor compound, after which it is separated and washed with an aliquot of a hydrocarbon until all chloride ions are gone.

[0042] In the solid catalyst component, the titanium compound, denoted Ti, is generally present in an amount of 0.5 to 10% by weight. The amount of electron donor compound remaining fixed on the solid catalyst component is generally 5 to 20 mol% relative to the magnesium dihalide.

[0043] Titanium compounds which can be used for the preparation of the solid catalyst component are titanium halides and halogen alcoholates. Titanium tetrachloride is the preferred compound.

[0044] The above reactions form magnesium halides in active form. Other reactions are known in the literature which, starting from magnesium compounds other than halides, such as magnesium carboxylates, form magnesium halides in active form.

[0045] Al-alkyl compounds used as co-catalysts include Al-trialkyls such as Al-triethyl, Al-triisobutyl, Al-tri-n-butyl and linear or cyclic Al-alkyl compounds containing two or more Al atoms bonded to each other via O or N atoms or SO4 or SO3 groups.

[0046] The Al-alkyl compound is generally used in such an amount that the Al / Ti ratio is 1 to 1000.

[0047] Electron donor compounds that can be used as external donors include aromatic acid esters, such as alkyl benzoates, and in particular silicon compounds containing at least one Si-OR bond, wherein R is a hydrocarbon radical.

[0048] Examples of silicon compounds are (tert-butyl)2Si(OCH3)2, (cyclohexyl)(methyl)Si(OCH3)2, (cyclopentyl)2Si(OCH3)2 and (phenyl)2Si(OCH3)2 and (1,1,2-trimethylpropyl)Si(OCH3)3.

[0049] 1,3-Diethers of the abovementioned formula can also be used advantageously. If the internal donor is one of these diethers, the external donor can be omitted.

[0050] In particular, component A) is preferably prepared by using a catalyst containing a phthalate as internal donor and (cyclopentyl)2Si(OCH3)2 as external donor, or the 1,3-diether as internal donor, even if many other combinations of the aforementioned catalyst components may allow the composition according to the invention to be obtained.

[0051] The polymerization is usually carried out at a temperature of 20°C to 120°C, preferably 40°C to 80°C. When the polymerization is carried out in the gas phase, the operating pressure is usually between 0.5MPa and 5MPa, preferably between 1MPa and 4MPa. In bulk polymerization, the operating pressure is usually 1-8MPa, preferably 1.5-5MPa. Hydrogen is usually used as a molecular weight regulator. The polymerization can be in the gas phase or in a slurry or in a solution. In one or more reactors. Preferably, the polymerization is carried out in two slurry reactors operated in series.

[0052] The molded article of the present disclosure may be, for example, an injection molded article, a blow molded article or a compression molded article. Preferably, the molded article of the present disclosure is a compression molded article.

[0053] The following examples are given to illustrate but not to limit the present disclosure.

[0054] Example

[0055] Characterization

[0056] Fractions insoluble and soluble in xylene at 25°C

[0057] The xylene soluble fraction has been measured according to ISO 16 152-2005; in the case of a solution volume of 250 ml, precipitation at 25° C. for 20 minutes, of which 10 minutes the solution was stirred (magnetic stirrer), and drying at 70°.

[0058] Melt flow rate (MFR)

[0059] Unless otherwise indicated, measurements are made according to ISO 1133 at 230°C and with a load of 21.6 kg.

[0060] Polydispersity (PI)

[0061] According to ISO 6721-10, a few grams of molten homopolymer are dynamically tested in a rate sweep at a temperature of 200°C with a parallel plate rheometer. G' (storage modulus) and G" (loss modulus) are measured as a function of frequency. From the rate sweep data, PI is defined by PI = 105 / Gc, where Gc is the crossover modulus as the modulus value at G' = G".

[0062] Melting temperature via differential scanning calorimetry (DSC)

[0063] The melting points (Tm) of the polymers were measured by differential scanning calorimetry (DSC) at 20°C / min on a Perkin Elmer DSC-1 calorimeter previously calibrated for the melting point of indium and according to ISO 11357-1, 2009 and 11357-3, 2011. The weight of the sample in each DSC crucible was kept at 6.0±0.5 mg.

[0064] To obtain the melting point, the weighed sample was sealed into an aluminum pan and heated to 200° C. at 20° C. / min. The sample was held at 200° C. for 2 minutes to allow all crystallites to melt completely, then cooled to 5° C. at 20° C. / min. After standing at 5° C. for 2 minutes, the sample was heated for a second run at 20° C. / min to 200° C. In this second heating run, the peak temperature (Tp,m) was taken as the melting temperature.

[0065] Homopolymer and propylene / ethylene copolymer 13 C NMR

[0066] 13 C NMR spectra were acquired on a Bruker AV-600 spectrometer equipped with a cryoprobe operating at 120 °C in Fourier transform mode at 160.91 MHz.

[0067] At 29.9ppm S ββ The peak of carbon (according to the nomenclature of "Monomer sequence distribution in ethylene-propylene rubber measured by 13C NMR. 3. Use of reaction probability models" CJ Carman, RA Harrington and CE Wilkes, Macromolecules, 1977, 10, 536) was used as an internal reference. The sample was dissolved in 1,1,2,2-tetrachloroethane-d2 at 8 wt / v% concentration at 120°C. Each spectrum was collected with a 90° pulse, with a delay of 15 seconds between the pulse and CPD to remove 1H-13C coupling. 512 transients were stored in 32K data points using a spectral window of 9000 Hz.

[0068] Evaluation of spectral assignments, triplet distribution, and composition was performed according to Kakugo ("Carbon-13 NMR determination of monomer sequence distribution in ethylene-propylene copolymers prepared with δ-titanium trichloride-diethylaluminum chloride" M. Kakugo, Y. Naito, K. Mizunuma, and T. Miyatake, Macromolecules, 1982, 15, 1150) using the following equation:

[0069] PPP=100T ββ / S PPE=100T βδ / S EPE=100T δδ / S

[0070] PEP=100s ββ / S PEE=100S βδ / S EEE=100(0.25S γδ +0.5S δδ ) / S

[0071] S=T ββ +T βδ +T δδ +S ββ +S βδ +0.25S γδ +0.5S δδ

[0072] The mole percent of ethylene content was estimated using the following equation:

[0073] E%mol=100*[PEP+PEE+EEE] The weight percentage of ethylene content is estimated using the following equation:

[0074]

[0075] Where P mol% is the molar percentage of propylene content, and MW E and MW P are the molecular weights of ethylene and propylene respectively.

[0076] The product of the reactivity ratios r1r2 is calculated according to Carman (CJ Carman, RA Harrington and CE Wilkes, Macromolecules, 1977; 10, 536) as:

[0077]

[0078] The stereoregularity of the propylene sequence is calculated according to PPP mmT ββ (28.90ppm to 29.65ppm) and full T ββ The ratio of (29.80 ppm to 28.37 ppm) was calculated as the mm content.

[0079] Intrinsic viscosity

[0080] The sample is dissolved by tetralin at 135°C and then poured into a capillary viscometer. The viscometer tube (Ubbelohde type) is surrounded by a cylindrical glass jacket; this setup allows temperature control with a circulating thermostatic liquid. The descent of the meniscus is timed by a photoelectric device. The passage of the meniscus in front of the upper lamp starts a counter with a quartz crystal oscillator. When passing the lower lamp, the meniscus stops the counter and the outflow time is recorded: this is converted into an intrinsic viscosity value by the Huggins equation, provided that the flow time of the pure solvent under the same experimental conditions (same viscometer and same temperature) is known. A single polymer solution is used to determine IV].

[0081] Melt Strength

[0082] The melt strength is measured according to ISO 16790-2005 by the Haul-off MeltStrength Meter produced by Geottfert Werkstoff Pruefmaschinen, Germany. The system measures the extension properties of a polymer melt by pulling a vertical melt strand at a constant pull-off speed or at a linear or exponentially accelerated speed. The HAUL-OFF system measures the force required to elongate the strand and calculates the elongation stress, pulling ratio, apparent elongation and viscosity. The polymer is melted and plasticized by a capillary rheometer and then extruded from a hole die with a diameter of 1 mm, a length of 30 mm and an inlet angle of 180°. The test is performed at 250°C. The distance from the capillary outlet to the center of the sensor pulley is 150 mm. In each temperature test, a force equal to 6 mm / s is applied. 2 The filaments are stretched with an acceleration of 100° and their elongation is measured by an angle sensor. In addition to the overall curve, the draw ratio (dimensionless value) and the force (cN) value are recorded as the final result. The value of the melt strength is the maximum force value of the curve.

[0083] Charpy impact test

[0084] Charpy impact test according to ISO 179-1eA and ISO 1873-2 measured on compression specimens

[0085] Tensile modulus

[0086] Tensile modulus measured on compression specimens according to ISO 527-2 and ISO 1873-2

[0087] Example 1 - Preparation of Homopolymer

[0088] Procedure for preparing solid catalyst components

[0089] The solid catalyst used in the following examples was prepared according to Example 10 of International Patent Application WO 00 / 63261. Triethylaluminium (TEAL) was used as cocatalyst and dicyclopentyldimethoxysilane was used as external donor in the weight ratios shown in Table 1.

[0090] polymerization

[0091] The polymerization operation is carried out in a series of two reactors in a continuous mode, which are equipped with means for transferring the product from one reactor to the one immediately adjacent thereto. The two reactors are liquid phase loop reactors. Propylene is the main solvent and hydrogen is used as a molecular weight regulator. The gas phase is continuously analyzed via gas chromatography.

[0092] At the end of the run, the powder was discharged and dried under a stream of nitrogen. The main polymerization conditions and polymer characteristics are reported in Tables 1 and 2.

[0093] Table 1 – Polymerization conditions

[0094] Example 1 TEAL / catalyst (weight ratio) 4.3 TEAL / external donor (weight ratio) 3 First Circuit Temperature ℃ 75 Pressure barg 40 <![CDATA[H2 ppmol]]> <10ppmol Separation weight % 50 Second Circuit Temperature ℃ 75 Pressure barg 40 <![CDATA[H2 ppmol]]> <10ppmol Separation weight % 50

[0095] The characteristics of the polymers of Example 1 and Comparative Example 2 are reported in Table 2

[0096] Table 2

[0097]

[0098]

[0099] *(230℃ / 2.16kg)

[0100] Comparative Example 2 is PP H2150 sold by LyondellBasell, a nucleated propylene homopolymer.

[0101] nm not measured

[0102] Abrasion tests according to ISO 15527:2007 have been measured at 250°C on compression moulded plaques produced with the polymers of Example 1 and Comparative Example 2. The results are reported in Table 3.

[0103] Table 3

[0104] Example 1 Comparative Example 2 Minimum wear index 375.9 394.6 Maximum wear index 413.9 418.0 Average wear index 351 361

Claims

1. A molded article comprising a propylene homopolymer, optionally containing up to 1.0 wt. % of ethylene-derived units, characterized in that: - the presence of two melting points in the DSC thermogram measured according to ISO 11357-3 at a heating and cooling rate of 20°C / min; - the higher melting point ranges from 155°C to 170°C measured according to ISO 11357-3 at a heating and cooling rate of 20°C / min; the fraction soluble in xylene at 25° C., measured according to ISO 16 152-2005, is comprised between 6.0% and 2.0% by weight; - as reported in the Examples section of the description, with C 13 The isotactic pentad mmmm% measured by NMR ranged from 96.5 mol% to 90.0 mol%; - an intrinsic viscosity (IV) measured in tetralin at 135° C. ranging from 5.5 dl / g to 12.0 dl / g; - at 250°C and at an applied speed equal to 6 mm / s 2 The melt strength measured according to ISO 16790-2005 under acceleration conditions is higher than 0.070N.

2. The molded article according to claim 1, wherein in the propylene homopolymer, two melting points exist in the DSC thermogram measured according to ISO 11357-3 at a heating and cooling rate of 20°C / min; and the lower melting point ranges from 135°C to 150°C.

3. The molded article according to claim 1 or 2, wherein in the propylene homopolymer, the higher melting point measured according to ISO 11357-3 at a heating and cooling rate of 20°C / min is in the range of 157°C to 168°C.

4. The molded article according to any of claims 1 to 3, wherein in the propylene homopolymer the fraction soluble in xylene at 25°C measured according to ISO 16 152-2005 is comprised between 5.0 wt.-% and 2.5 wt.-%.

5. The molded article according to any of claims 1 to 4, wherein in the propylene homopolymer the fraction soluble in xylene at 25°C measured according to ISO 16 152-2005 is comprised between 4.0 and 2.8 wt%.

6. The molded article according to any one of claims 1 to 5, wherein in the propylene homopolymer, 13 The isotactic pentad mmmm% measured by C-NMR ranges from 96.0 mol% to 93.0 mol%.

7. The molded article according to any one of claims 1 to 6, wherein in the propylene homopolymer, 13 The isotactic pentad mmmm% measured by C-NMR ranges from 95.5 mol% to 93.5 mol%.

8. The molded article according to any one of claims 1 to 7, wherein in the propylene homopolymer, the intrinsic viscosity (IV) measured in tetralin at 135°C is in the range of 7.0 dl / g to 11.0 dl / g.

9. The molded article according to any one of claims 1 to 8, wherein in the propylene homopolymer, the intrinsic viscosity (IV) measured in tetralin at 135°C is in the range of 8.0 dl / g to 10.0 dl / g.

10. The molded article according to any one of claims 1 to 1, wherein at 250°C and under an applied pressure equal to 6 mm / s 2 The melt strength measured according to ISO 16790-2005 under acceleration of 0.080N is higher.

11. The molded article T according to any one of claims 1 to 10, the propylene homopolymer according to any one of claims 1 to 10, wherein at 250°C and at an applied pressure equal to 6 mm / s 2 The melt strength measured according to ISO 16790-2005 under acceleration of 1.5 N is higher than 0.090 N.

12. The molded article T according to any one of claims 1 to 11, wherein the propylene homopolymer has an average abrasion index value below 355 measured according to ISO 15527:2007 on compression molded plaques.

13. The propylene homopolymer according to any one of claims 1 to 12, which is not nucleated.

14. The molded article according to any one of claims 1 to 13, which is an injection molded article, a blow molded article or a compression molded article.

15. A compression molded article comprising the propylene homopolymer according to claims 1 to 13.

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