Claims
- 1. A polypropylene composition, in the form of spheroidal flowable particles, obtained by sequential polymerization in at least two steps wherein components (B) and (C) are polymerized in the presence of component (A) polymerized in the first step, comprising;
- (A) 10-60 parts by weight of homopolymer polypropylene with isotactic index greater than 90, or of crystalline propylene copolymer with ethylene, with a CH.sub.2 .dbd.CHR olefin where R is a 2-6 carbon alkyl radical, or combinations thereof, containing over 85% by weight of propylene and having an isotactic index greater than 85;
- (B) 10-40 parts by weight of a crystalline, polymer fraction containing ethylene and propylene, having an ethylene content of from about 52.4% to about 74.6% and insoluble in xylene at room temperature;
- (C) 30-60 parts by weight of an amorphous ethylene-propylene copolymer fraction containing optionally small proportions of a diene, soluble in xylene at room temperature and containing 40 to 70% by weight ethylene;
- said composition having a flex modulus smaller than 700 MPa, tension set at 75% less than 60%, tensile stress greater than 6 Mpa and notched Izod resilience at -20.degree. and -40.degree. C. greater than 600 J/m.
- 2. The composition of claim 1 where the total content of polymerized ethylene is between 20 and 60% by weight.
- 3. The compositions of claim 1 or 2 where the flex modulus is between 200 and 500 MPa, the tension set between 20 and 50%, and the tensile stress between 8 and 20 MPa.
- 4. The composition of claim 1 in the form of spheroidal particles with average diameter between 500 and 7000 .mu.m, flowability less than 30 seconds and tamped bulk density greater than 0.4 g/cc.
- 5. A manufactured article obtained from the composition of claim 1.
Priority Claims (1)
| Number |
Date |
Country |
Kind |
| 20328 A/89 |
Apr 1989 |
ITX |
|
DETERMINATION OF THE PERCENTAGE SOLUBLE IN XYLENE
This application is a continuation of application Ser. No. 07/515,936, filed Apr. 27, 1990, now abandoned.
This invention refers to thermoplastic polypropylene compositions having elastomeric properties, obtained in the form of spheroidal particles, endowed with specific flowability and apparent density characteristics, and to their preparation method.
During the last few years, polypropylene compositions having elastic properties while maintaining the capability of being transformed into manfuactured articles using the same apparatus and process normally used for thermoplastic materials, have gained more and more importance.
Said compositions, sometimes referred to as polyolefin thermoplastic elastomers, have found application above all in the automotive, electric cables and sporting goods fields. Because of their advantageous performances, they tend to replace the more expensive thermoplastic styrene and butadiene based rubbers.
The compositions are prepared by mixing, under dynamic vulcanization conditions, ethylene-propylene rubbers (EPR), or ethylene-propylene-diene rubbers (EPDM), with crystalline polyolefins, in particular polypropylene.
Such a preparation process involves a considerable use of energy and the mechanical homogeneity of the components is not always such to impart the desired balance of optimum properties to the final product.
Therefore, the need is felt to be able to produce polyolefin compositions with the desired balance of elasto-plastic properties through polymerization processes.
A method for the preparation of polymer products having elasto-plastic properties directly in the polymerization phase is described in U.S. Pat. No. 4,298,721.
The thermoplastic elastomers described in such a patent are obtained by polymerizing ethylene-propylene mixtures using specific types of catalysts supported on magnesium halides. The copolymers obtained in this manner have elasto-plastic properties, but are not heat resistant, since they have a relatively low melting point (around 100.degree.-130.degree. C.).
U.S. Pat. No. 4,489,195 describes the preparation of polyolefin thermoplastic elastomers in two stages of polymerization using stereospecific catalysts supported on magnesium halides; in the first stage homopolymer polypropylene is formed, and in the second, carried out preferably in gas phase, an elastomeric ethylene/propylene copolymer.
In order to prevent agglomeration of the particles, the temperature in the second stage is kept relatively low (under 50.degree. C.). The polymer is obtained in powder form.
The need to operate at a relatively low temperature in the rubber copolymer formation stage penalizes the process from the point of view of the thermal exchange as well as the diminished productivity of the catalyst. According to the data furnished in the patent, the composition do not include ethylene polymeric fractions insoluble in xylene at room temperature.
U.S. Pat. No. 4,491,652 describes the preparation of polypropylene thermoplastic elastomers in two stages, where in the first stage the propylene is polymerized to homopolymer polypropylene, and in the second one mixtures of ethylene-propylene are polymerized to form rubbery copolymers. The second stage is carried out in the presence of a solvent at temperatures of 60.degree.-80.degree. C. Operating at this temperature, one obtains partial dissolution of the rubbery copolymer with the formation of lumps which must then disintegrated. According to the patent the disintegration is done by grinding. As a matter of fact, it is known that when the percentage of the rubbery ethylene-propylene copolymer exceeds about 20% of the total polymer, it is impossible to avoid the agglomeration of the particles even when the operation takes place in the presence of stereospecific catalysts (see European published patent application 0029651 and Belgian patent 876,413).
The agglomeration phenomenon is particularly critical when the ethylene-propylene copolymerization stage is done in gas phase. The fouling of the reactors prevents in practice to carry out the process in gas phase.
Now unexpectedly it has been found that using specific catalysts supported on magnesium chloride it is possible to obtain, even with processes in gas phase, polypropylene compositions with plasto-elastic properties, in the form of spheroidal particles having flowability and bulk density characteristics sufficiently elevated and such as to allow the use of same in normal processes of transformation to products without having to resort to preliminary granulation operations.
The compositions, as a result of to their plasto-elastic characteristics, are suitable for all applications foreseen for traditional thermoplastic polyolefin elastomers.
Moreover, since the composition are obtained under conditions where the rubbery phase which is formed is distributed uniformly in the polypropylene matrix, they provide properties superior to the corresponding compositions obtained by mechanical mixing of components.
Finally, since the compositions are obtained with very highly active catalysts, the amount of catalyst residue in said compositions is so small that the removal of catalysts residues is not necessary.
The compositions of the invention include:
The total content of the polymerized ethylene is between 20 and 60% by weight.
The molecular weight of the various fractions (determined by measuring intrinsic viscosity in tetrahydronaphthalene at 135.degree. C.) varies depending on the nature of the components and the melt index of the final product. It is comprised within the following preferred limits:
As already indicated the compositions are obtained in the form of spheroidal particles having an average diameter between 500 and 7000 .mu.m, flowability (at 70.degree. C.) lower than 30 seconds; bulk density (tamped) greater than 0.4 g/cc, in particular between 0.4 and 0.6 g/cc.
The compositions present at least one melting peak determined at DSC at temperatures higher than 140.degree. C.; flex modulus lower than 700 MPa, preferably between 200 and 500 MPa; VICAT softening point greater than 50.degree. C.; Shore A hardness greater than 80 and Shore D hardness greater than 30; tension set at 75% lower than 60%, in particular between 20 and 50%; tensile stress greater than 6 MPa, in particular between 8 and 20 MPa.
The examination of the compositions under electronic microscope indicates that the phase dispersed is constituted by amorphous ethylene-propylene copolymer and has an average particle size smaller than 2 .mu.m.
The manufactured articles that can be obtained from the composition find application particularly in the automotive, electrical cables and sporting goods fields.
The compositions are prepared with a polymerized process including at least two stages, where in the first stage the propylene is polymerized to form component A), and in the following stages the ethylene-propylene mixtures are polymerized to form components B) and C).
The operation takes place in liquid or gas phase, or in liquid-gas phase.
A preferred process consists in carrying out the propylene homopolymerization stage using as a diluent the liquid propylene, and the copolymerization stage of the propylene and ethylene in gas phase without intermediate stages except for the partial degassing of the propylene.
The polymerization of the propylene may be done in the presence of ethylene or an alpha olefin such as butene-1, pentene-1, 4-methylpentene-1, in such quantities that the isotactic index of the resulting product is greater than 85%.
The copolymerization of the propylene and the ethylene can also occur in the presence of another alpha-olefin or a diene, conjugated or not, such as butadiene, 1,4-hexadiene, 1,5-hexadiene, ethylidene-norbornene-1.
The reaction temperature in the propylene polymerization stage and in the propylene and ethylene copolymerization stage may be equal or different, and is comprised generally between 40.degree. C. and 90.degree. C., preferably 50.degree.-80.degree. C. in case of homopolymerization and 50.degree.-70.degree. C. in case of copolymerization.
The pressure of the first stage is the one that competes with vapor pressure of the liquid propylene at the working temperature, possibly modified by the vapor pressure of the small quantity of inert diluent used to feed the catalytic mixture and the hydrogen overpressure as regulator of the molecular weight.
The pressure relative to the copolymerization stage, if done in gas phase, can be between 5 and 30 atm. The stay time relative to the two stages vary depending on the desired rapport between the homopolymer fraction and the bipolymer B and C ones, and are generally between 30 minutes and 8 hours. Known traditional chain transfer agents, such as hydrogen and ZnEt.sub.2, can be used as molecular weight regulators.
The catalyst used in the polymerization includes the reaction product of a solid compound containing a titanium compound and an electron-donor compound (internal donor) supported on magnesium chloride, with an Al-trialkyl compound and an electron-donor compound (external donor).
In order to obtain the compositions of the invention in the form of flowable particles, having high bulk density, it is critical that the solid catalyst component presents the following properties:
The catalyst component is prepared following the method described below.
A magnesium chloride adduct with alcohol containing generally 3 moles of alcohol for mole of MgCl.sub.2, is obtained in the form of spherical particles by emulsifying the molten adduct in an inert hydrocarbon liquid immiscible with the adduct, and then cooling the emulsion very quickly in order to cause the adduct ot solidify in spherical particle form.
The particles are then submitted to partial dealcoholization with a heating cycle between 50.degree. and 130.degree.C. which brings the alcohol content from 3 to 1-1.5 moles per mole of MgCl.sub.2.
The adduct is then suspended in TiCl.sub.4 cold, in a concentration of 40-50 g/l and consequently brought to a temperature of 80.degree.-135.degree. C. at which it is maintained for a period of 1-2 hr.
To the TiCl.sub.4 is also added an electron-donor compound selected preferably among the alkyl, cycloalkyl or aryl phthalates such as for instance diisobutyl, di-n-butyl and di-n-octyl phthalate.
The excess of TiCl.sub.4 is separated hot through filtration or sedimentation, and the treatment with TiCl.sub.4 is repeated one or more times; the solid is then washed with heptane or hexane and dried.
The catalyst component thus obtained presents the following characteristics:
The catalyst is obtained by mixing the catalyst component with an Al-trialkyl compound, preferably Al-triethyl and Al-triisobutyl, and an electron-donor compound selected preferably among silane compounds of the formula R'R"Si(OR).sub.2 where R' and R", equal or different, are alkyl, cycloalkyl or aryl radicals containing 1-18 carbon atoms, and R is a 1-4 carbon alkyl radical.
Typical silanes are diphenyldimethoxysilane, dicyclohexyldimethoxysilane, methyl-tert-butyldimethoxysilane and diisopropyldimethoxysilane.
Silane compounds such as phenyltriethoxysilane can also be used.
The Al/Ti ratio is usually between 10 and 200 and the silane/Al molar ratio between 1/5 and 1/50.
The catalysts may be precontacted with small quantities of olefin (prepolymerization), maintaining the catalyst in suspension in a hydrocarbon solvent and polymerizing at a temperature between room temperature and 60.degree. C., and producing a quantity of polymer from 0.5 to 3 times the weight of the catalyst.
The operation can occur in liquid monomer also, producing in this case a quantity of polymer up to 1000 times the catalyst weight.
The data reported in the examples and text relative to the properties listed below have been determined by using the following methods:
The samples to be submitted to the various physico-mechanical tests have been molded directly from the in polymer in the form of spherical particles, previously stabilized with 0.1% by weight of IRGANOX.sup.R 1010 and 0.1% by weight of BHT (2,6-di-tert-butyl-paracresol), under the following conditions and using a GBF V160 injection press:
The percentage by weight of total bipolymer (% Bp=% C+% B) is calculated by determining the weight of the propylene-ethylene mixture fed in the second stage and comparing it to the weight of the final product.
The weight percentages of the three fractions A, B and C, described in the text, are determined in the following manner:
The percentage by weight of ethylene contained in copolymer fraction C soluble in xylene has been calculated with the following formula: ##EQU1## where C.sub.F =% wt. ethylene in the soluble in xylene of the final product;
2.5 g of polymer are dissolved in 250 ml of xylene at 135.degree. C. under agitation. After 20 minutes the solution is left to cool down to 25.degree. C., still agitating, and then left to rest for 30 minutes.
The precipitate is filtered with filter paper; the solution is evaporated in nitrogen current and the residual under vacuum dried at 80.degree. C. until it reaches constant weight. In this manner the percentage by weight of polymer soluble in xylene at room temperature is calculated. The percentage by weight of polymer insoluble in xylene at room temperature is considered as the isotactic index of the polymer. The value thus obtained coincides substantially with the isotactic index determined via extraction with boiling n-heptane, which by definition constitutes the isotactic index of the polypropylene.
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Continuations (1)
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Number |
Date |
Country |
| Parent |
515936 |
Apr 1990 |
|
Patent Grant
5302454
