Process for manufacture of low emission heterophasic polypropylene

Abstract

The invention relates to a process for the preparation of a heterophasic propylene copolymer consisting of a propylene-based matrix and a dispersed ethylene-a-olefin copolymer, comprising the steps of a) preparing the propylene-based matrix from propylene and optionally a C2 or C4-C12 α-olefin by contacting at least propylene and optionally C2 or C4-C12 a-olefin with a catalyst in a first gas-phase reactor at a temperature T1 and a pressure P1, b) subsequently preparing the dispersed ethylene-α-olefin copolymer from ethylene and a C3-C12 α-olefin by contacting the ethylene and the C3-C12 α-olefin with a catalyst in a second gas-phase reactor at a temperature T2 and a pressure P2, wherein T1-T2 is in the range from 6 to 25° C., wherein T1>T2, wherein PI and P2 are in the range from 22 to 30 bar to prepare a heterophasic propylene copolymer (A′).

Claims

1. The process for the preparation of a heterophasic propylene copolymer consisting of a propylene-based matrix and a dispersed ethylene-α-olefin copolymer, comprising the steps of a) preparing the propylene-based matrix from propylene and optionally a C2 or C4-C12 α-olefin by contacting at least propylene and optionally C2 or C4-C12 α-olefin with a catalyst in a first gas-phase reactor at a temperature T1 and a pressure P1, b) subsequently preparing the dispersed ethylene-α-olefin copolymer from ethylene and a C3-C12 α-olefin by contacting the ethylene and the C3-C12 α-olefin with a catalyst in a second gas-phase reactor at a temperature T2 and a pressure P2, wherein T1-T2 is in the range from 6 to 25° C., wherein T1>T2, wherein P1 and P2 are in the range from 22 to 30 bar, to prepare a heterophasic propylene copolymer (A′).

2. The process according to claim 1, wherein the melt flow rate of the heterophasic propylene copolymer (A′) is in the range of 1.0 to 20.0 dg/min a measured according to ISO1133 (2.16 kg, 230° C.) and/or wherein the FOG value of the heterophasic propylene copolymer (A′) is at most 500 μg/g, as determined by VDA 278.

3. The process according to claim 1, wherein the temperature T1 in the first gas-phase reactor is in the range from 60 to 75° C., or wherein the temperature T1 in the first gas-phase reactor is in the range from 70 to 85° C.

4. The process according to claim 1, wherein in step a) the propylene-based matrix is prepared by contacting the propylene, optional C2 or C4-C12 α-olefin and a prepolymer in the first gas phase reactor, wherein the prepolymer is prepared by contacting propylene and optional α-olefin with a catalyst in a prepolymerization reactor.

5. The process according to claim 1, wherein the catalyst in step a) and/or step b), is a catalyst system which comprises a Ziegler-Natta catalyst and at least one external electron donor.

6. The process according to claim 1, wherein the heterophasic propylene copolymer consists of (a) a propylene-based matrix, wherein the propylene-based matrix consists of a propylene homopolymer and/or a propylene-α-olefin copolymer consisting of at least 90 wt % of propylene and at most 10 wt % of α-olefin, based on the total weight of the propylene-based matrix and wherein the propylene-based matrix is present in an amount of 60 to 95 wt % based on the total heterophasic propylene copolymer and (b) a dispersed ethylene-α-olefin copolymer, wherein the dispersed ethylene-α-olefin copolymer is present in an amount of 40 to 5 wt % based on the total heterophasic propylene copolymer and wherein the sum of the total amount of propylene-based matrix and total amount of the dispersed ethylene-α-olefin copolymer in the heterophasic propylene copolymer is 100 wt %.

7. The process according to claim 1, wherein the amount of ethylene in the ethylene-α-olefin copolymer is in the range of 20-65 wt % based on the ethylene-α-olefin copolymer.

8. The process according to claim 1, wherein the α-olefin in the ethylene-α-olefin copolymer is chosen from the group of α-olefins having 3 to 8 carbon atoms and any mixtures thereof.

9. The process according to claim 1, wherein the propylene-based matrix consists of a propylene homopolymer.

10. The process according to claim 1, further comprising the subsequent step of (II) visbreaking heterophasic propylene copolymer (A′), to obtain a heterophasic propylene copolymer (A) having a melt flow rate that is higher than the melt flow rate of the heterophasic propylene copolymer (A′) as measured according to ISO01133 (2.16 kg, 230° C.).

11. The process for preparation of a heterophasic propylene copolymer according to claim 10, wherein the melt flow rate of the heterophasic propylene copolymer (A) as measured according to ISO1133 (2.16 kg, 230° C.) is in the range from 20 to 90 dg/min.

12. The process for preparation of a heterophasic propylene copolymer according to claim 10, wherein the FOG value of the heterophasic propylene copolymer (A) is at most 700 μg/g, as determined by VDA 278.

13. The process for the preparation of a heterophasic propylene copolymer according to claim 10, further comprising the step of III) reducing the FOG value of the heterophasic propylene copolymer (A′) and/or the heterophasic propylene copolymer (A) by maintaining the heterophasic propylene copolymer (A′) and/or the heterophasic propylene copolymer (A) at such temperature and for such time as to allow reduction of the FOG value to the desired level to produce a heterophasic propylene copolymer (B′) and/respectively a heterophasic propylene copolymer (B).

14. The process for the preparation of a heterophasic propylene copolymer according to claim 1, wherein the first and second gas-phase reactors are horizontal stirred gas-phase reactors.

15. The process according to claim 5, wherein the catalyst system is obtained by a catalyst preparation process comprising the steps of: (A) providing a procatalyst obtainable via a process comprising the steps of: i) contacting a compound R.sup.4.sub.zMgX.sup.4.sub.2-z with an alkoxy- or aryloxy-containing silane compound to give a first intermediate reaction product, being a solid Mg(OR.sup.1).sub.xX.sup.1.sub.2-x, wherein: R.sup.4 is the same as R.sup.1 being a linear, branched or cyclic hydrocarbyl group independently selected from alkyl, alkenyl, aryl, aralkyl, alkoxycarbonyl or alkylaryl groups, and one or more combinations thereof; wherein said hydrocarbyl group may be substituted or unsubstituted, may contain one or more heteroatoms; X.sup.4 and X.sup.1 are each independently selected from the group of consisting of fluoride (F—), chloride (Cl—), bromide (Br—) or iodide (I—); ii) optionally contacting the solid Mg(OR.sup.1).sub.xX.sub.2-x obtained in step i) with at least one activating compound selected from the group formed of activating electron donors and metal alkoxide compounds of formula M.sup.1(OR.sup.2).sub.v-w(OR.sup.3).sub.w or M.sup.2(OR.sup.2).sub.v-w(R.sup.3).sub.w, to obtain a second intermediate product; wherein M.sup.1 is a metal selected from the group consisting of Ti, Zr, Hf, Al or Si; M.sup.2 is a metal being Si; v is the valency of M.sup.1 or M.sup.2; R.sup.2 and R.sup.3 are each a linear, branched or cyclic hydrocarbyl group independently selected from alkyl, alkenyl, aryl, aralkyl, alkoxycarbonyl or alkylaryl groups, and one or more combinations thereof; wherein said hydrocarbyl group may be substituted or unsubstituted, may contain one or more heteroatoms; iii) contacting the first or second intermediate reaction product, obtained respectively in step i) or ii), with a halogen-containing Ti-compound and optionally an internal electron donor to obtain said procatalyst; B) contacting said procatalyst with a co-catalyst and the at least one external electron donor to form a catalyst.

16. The process according to claim 1, wherein the melt flow rate of the heterophasic propylene copolymer (A′) is in the range of 1.0 to 20.0 dg/min a measured according to ISO1133 (2.16 kg, 230° C.) and wherein the FOG value of the heterophasic propylene copolymer (A′) is at 400 μg/g, as determined by VDA 278, wherein the temperature T1 in the first gas-phase reactor is in the range from 65 to 72° C. or wherein the temperature T1 in the first gas-phase reactor is in the range from 73 to 80° C., wherein in step a) the propylene-based matrix is prepared by contacting the propylene, optional C2 or C4-C12 α-olefin and a prepolymer in the first gas phase reactor, wherein the prepolymer is prepared by contacting propylene and optional α-olefin with a catalyst in a prepolymerization reactor, wherein the catalyst in step a) and step b), is a catalyst system which comprises a Ziegler-Natta catalyst and at least one external electron donor, which external electron donor is chosen from the group of a compound having a structure according to Formula III (R.sup.90).sub.2N—Si(OR.sup.91).sub.3, a compound having a structure according to Formula IV: (R.sup.92)Si(OR.sup.93).sub.3 and mixtures thereof, wherein each of R.sup.90, R.sup.91, R.sup.92 and R.sup.93 groups are each independently a linear, branched or cyclic, substituted or unsubstituted alkyl having between 1 and 10 carbon atoms, wherein the catalyst system is obtained by a catalyst preparation process comprising the steps of: A) providing a procatalyst obtainable via a process comprising the steps of: i) contacting a compound R.sup.4.sub.zMgX.sup.4.sub.2-z with an alkoxy- or aryloxy-containing silane compound to give a first intermediate reaction product, being a solid Mg(OR.sup.1).sub.xX.sup.1.sub.2-x, wherein: R.sup.4 is the same as R.sup.1 being a linear, branched or cyclic hydrocarbyl group independently selected from alkyl, alkenyl, aryl, aralkyl, alkoxycarbonyl or alkylaryl groups, and one or more combinations thereof; wherein said hydrocarbyl group may be substituted or unsubstituted, may contain one or more heteroatoms; X.sup.4 and X.sup.1 are each independently selected from the group of consisting of fluoride (F—), chloride (Cl—), bromide (Br—) or iodide (I—); ii) contacting the solid Mg(OR.sup.1).sub.xX.sub.2-x, obtained in step i) with at least one activating compound selected from the group formed of activating electron donors and metal alkoxide compounds of formula M.sup.1(OR.sup.2).sub.v-w(OR.sup.3), or M.sup.2(OR.sup.2).sub.v-w(R.sup.3).sub.w, to obtain a second intermediate product; wherein M.sup.1 is a metal selected from the group consisting of Ti, Zr, Hf, Al or Si; M.sup.2 is a metal being Si; v is the valency of M.sup.1 or M.sup.2; R.sup.2 and R.sup.3 are each a linear, branched or cyclic hydrocarbyl group independently selected from alkyl, alkenyl, aryl, aralkyl, alkoxycarbonyl or alkylaryl groups, and one or more combinations thereof; iii) contacting the first or second intermediate reaction product, obtained respectively in step i) or ii), with a halogen-containing Ti-compound and optionally an internal electron donor to obtain said procatalyst; B) contacting said procatalyst with a co-catalyst and the at least one external electron donor to form a catalyst; wherein the heterophasic propylene copolymer consists of (a) a propylene-based matrix, wherein the propylene-based matrix consists of a propylene homopolymer and/or a propylene-α-olefin copolymer consisting of at least 90 wt % of propylene and at most 10 wt % of α-olefin, based on the total weight of the propylene-based matrix, and wherein the propylene-based matrix is present in an amount of 60 to 95 wt % based on the total heterophasic propylene copolymer and (b) a dispersed ethylene-α-olefin copolymer, wherein the dispersed ethylene-α-olefin copolymer is present in an amount of 40 to 5 wt % based on the total heterophasic propylene copolymer and wherein the sum of the total amount of propylene-based matrix and total amount of the dispersed ethylene-α-olefin copolymer in the heterophasic propylene copolymer is 100 wt %.

17. The process according to claim 1, wherein the amount of ethylene in the ethylene-α-olefin copolymer is in the range of 20-65 wt % based on the ethylene-α-olefin copolymer, wherein the α-olefin in the ethylene-α-olefin copolymer is chosen from the group of α-olefins having 3 to 8 carbon atoms and any mixtures thereof, preferably wherein the α-olefin in the ethylene-α-olefin copolymer is propylene, and wherein the propylene-based matrix consists of a propylene homopolymer, further comprising the subsequent step of (II) visbreaking heterophasic propylene copolymer (A′), to obtain a heterophasic propylene copolymer (A) having a melt flow rate that is higher than the melt flow rate of the heterophasic propylene copolymer (A′) as measured according to ISO1133 (2.16 kg, 230° C.), preferably wherein the shifting ratio, which is the ratio of the melt flow rate of the heterophasic propylene copolymer (A) to the melt flow rate of the heterophasic propylene copolymer (A′) is in the range from 2 to 10.

Description

EXAMPLES

(1) Measurements

(2) Melt Flow Rate

(3) Melt flow rate was determined in accordance with ISO 1133 at 230° C. and 2.16 kg.

(4) RC, RCC2

(5) RC is the rubber content (ethylene-propylene copolymer, so-called rubber phase) in the heterophasic propylene copolymer; RCC2 is the ethylene content in the rubber part of the heterophasic propylene copolymer. RC and RCC2 were measured using .sup.13C-NMR according to known procedures.

(6) FOG

(7) FOG was determined according to VDA 278:2011 from pellets. FOG according to VDA 278 is the sum of all organic compounds of low volatility, which have an elution time greater than or equal to n-tetradecane. FOG is calculated as tetradecane equivalent (TE). FOG according to VDA 278 represents organic compounds in the boiling point range of n-alkanes C.sub.14 to C.sub.32. VDA standards are issued by “Verband der Automobilindustrie”. The VDA standards used herein are available from Dokumentation Kraftfahrwesen (DKF); Ulrichstrasse 14, D-74321 Bietigheim-issingen, Germany or can be downloaded from their website (www.dkf-ev.de). Immediately after peroxide shifting (step II), samples were taken and sealed in Lamigrip aluminium bags from Fisher Scientific. The FOG values were measured within a week from sealing the bags. To allow a direct comparison, all VDA278 measurements were carried out on the same GC equipment.

(8) Experimental

(9) Catalyst I

(10) Catalyst I is prepared according to the method disclosed in U.S. Pat. No. 4,866,022, hereby incorporated by reference. This patent discloses a catalyst component comprising a product obtained by: (a) forming a solution of a magnesium-containing species from a magnesium carbonate or a magnesium carboxylate; (b) precipitating solid particles from such magnesium-containing solution by treatment with a transition metal halide and an organosilane having a formula: R.sub.nSiR′.sub.4-n, wherein n=0 to 4 and wherein R is hydrogen or an alkyl, a haloalkyl or aryl radical containing one to about ten carbon atoms or a halosilyl radical or haloalkylsilyl radical containing one to about eight carbon atoms, and R′ is OR or a halogen; (c) reprecipitating such solid particles from a mixture containing a cyclic ether; and (d) treating the reprecipitated particles with a transition metal compound and an electron donor. This process for preparing a catalyst is incorporated into the present application by reference.

(11) Catalyst II

(12) A. Grignard Formation Step

(13) A stirred flask, fitted with a reflux condenser and a funnel, was filled with magnesium powder (24.3 g). The flask was brought under nitrogen. The magnesium was heated at 80° C. for 1 hour, after which dibutyl ether (DBE, 150 ml), iodine (0.03 g) and n-chlorobutane (4 ml) were successively added. After the colour of the iodine had disappeared, the temperature was raised to 80° C. and a mixture of n-chlorobutane (110 ml) and dibutyl ether (750 ml) was slowly added for 2.5 hours. The reaction mixture was stirred for another 3 hours at 80° C. Then the stirring and heating were stopped and the small amount of solid material was allowed to settle for 24 hours. By decanting the colorless solution above the precipitate, a solution of butylmagnesiumchloride (reaction product of step A) with a concentration of 1.0 mol Mg/l was obtained.

(14) B. Preparation of the Intermediate Reaction Product

(15) 250 mL of dibutyl ether was introduced to a 1 L reactor fitted with a propeller stirrer and two baffles. The reactor was thermostated at 35° C. and the stirrer speed was kept at 200 rpm. Then a cooled (to 15° C.) 360 mL solution of the Grignard reaction product as prepared in A and 180 ml of a cooled (to 15° C.) solution of 38 ml of tetraethoxysilane (TES) in 142 ml of DBE were dosed into the reactor for 400 min. with preliminary mixing in a minimixer of 0.15 ml volume, which was cooled to 15° C. by means of cold water circulating in the minimixer jacket. The premixing time was 18 seconds in the minimixer and the connecting tube between the minimixer and the reactor. The stirring speed in the minimixer was 1000 rpm. On the dosing completion, the reaction mixture was kept at 35° C. for 0.5 hours. Then the reactor was heated to 60° C. and kept at this temperature for 1 hour. Then the stirring was stopped and the solid substance was allowed to settle. The supernatant was removed by decanting. The solid substance was washed three times using 300 ml of heptane. As a result, a white solid reaction product was obtained and suspended in 200 ml of heptane.

(16) Under an inert nitrogen atmosphere at 20° C. a 250 ml glass flask equipped with a mechanical agitator is filled with a slurry of 5 g of the reaction product of step B dispersed in 60 ml of heptane. Subsequently, a solution of 0.86 ml methanol (MeOH/Mg=0.5 mol) in 20 ml heptane is dosed under stirring during 1 hour. After keeping the reaction mixture at 200° C. for 30 minutes the slurry was slowly allowed to warm up to 300° C. for 30 min and kept at that temperature for another 2 hours. Finally the supernatant liquid is decanted from the solid reaction product which was washed once with 90 ml of heptane at 300° C.

(17) C. Preparation of the Catalyst

(18) A reactor was brought under nitrogen and 125 ml of titanium tetrachloride was added to it. The reactor was heated to 90° C. and a suspension, containing about 5.5 g of the support obtained in step C in 15 ml of heptane, was added to it under stirring. The reaction mixture was kept at 90° C. for 10 min. Then ethyl benzoate was added (EB/Mg=0.15 molar ratio). The reaction mixture was kept for 60 min. Then the stirring was stopped and the solid substance was allowed to settle. The supernatant was removed by decanting, after which the solid product was washed with chlorobenzene (125 ml) at 90° C. for 20 min. The washing solution was removed by decanting, after which a mixture of titanium tetrachloride (62.5 ml) and chlorobenzene (62.5 ml) was added. The reaction mixture was kept at 90° C. for 30 min. After which the stirring was stopped and the solid substance was allowed to settle. The supernatant was removed by decanting, after which a mixture of titanium tetrachloride (62.5 ml) and chlorobenzene (62.5 ml) was added. Then di-n-butyl phthalate (DBP) (DBP/Mg=0.15 molar ratio) in 3 ml of chlorobenzene was added to reactor and the temperature of reaction mixture was increased to 115° C. The reaction mixture was kept at 115° C. for 30 min. After which the stirring was stopped and the solid substance was allowed to settle. The supernatant was removed by decanting, after which a mixture of titanium tetrachloride (62.5 ml) and chlorobenzene (62.5 ml) was added. The reaction mixture was kept at 115° C. for 30 min, after which the solid substance was allowed to settle. The supernatant was removed by decanting and the solid was washed five times using 150 ml of heptane at 600° C., after which the catalyst III, suspended in heptane, was obtained.

(19) Catalyst III

(20) Catalyst III is prepared according to the method described in U.S. Pat. No. 5,093,415 of Dow, hereby incorporated by reference. This patent discloses an improved process to prepare a catalyst including a reaction between titanium tetrachloride, diisobutyl phthalate, and magnesium diethoxide to obtain a solid material. This solid material is then slurried with titanium tetrachloride in a solvent and phthaloyl chloride is added. The reaction mixture is heated to obtain a solid material which is reslurried in a solvent with titanium tetrachloride. Again this was heated and a solid collected. Once again the solid was reslurried once again in a solution of titanium tetrachloride to obtain a catalyst.

(21) Propylene Homopolymer Polymerization Experiments

(22) Polymerization experiments of propylene homopolymers (Table 1) were performed on a bench-scale gas-phase reactor using catalysts I, II and III described above at different reaction temperatures (50, 60, 70 and 80° C.) as well as with different external electron donors in order to determine the effect of the reaction temperature on the FOG emission values of the propylene homopolymers. The pressure used was 22 bar. Triethylaluminium was used as co-catalyst, and two external electron donors were employed; di(iso-propyl) dimethoxysilane (DiPDMS) and n-propyltriethoxysilane (nPTES). Homopolymers produced at a temperature of 60° C. are denoted with CE as comparative experiments. Homopolymers produced at 50, 70 and 80° C. are denoted with RE as reference experiments of the present invention. RE and CE show the effects of the reaction temperature on the FOG emission values of polypropylene. At a given reaction temperature (T.sub.R1, also referred in the present invention as T1), propylene homopolymers of melt flow rate 50 dg/min were produced at different H2/C3 molar ratios, due to the different hydrogen sensitivity of the external donors. H2/C3 is the molar ratio of hydrogen to propylene in the gas cap of the reactor, measured by on-line gas chromatography.

(23) TABLE-US-00001 TABLE 1 Polymerization and FOG data of propylene homopolymers of melt flow rate 50 dg/min T.sub.R1 H.sub.2/C.sub.3 FOG Exp # Catalyst External Donor ° C. mol/mol μg/g CE1 I nPTES 60 0.029 710 RE1 I nPTES 80 0.0157 490 CE2 II DiPDMS 60 0.061 665 RE2 II DiPDMS 80 0.049 585 CE3 III DiPDMS 60 0.048 590 RE3 III DiPDMS 80 0.029 510 RE41 III nPTES 50 0.026 410 CE4 III nPTES 60 0.022 290 RE42 III nPTES 70 0.013 250 RE43 III nPTES 80 0.0054 190

(24) From Table 1, it is clear that for a given melt flow of the propylene homopolymer, the increase in T.sub.R1 reduces the FOG value, and this effect is independent of the catalyst/external donor system.

(25) From Table 1, it is also shown that nPTES as compared to other external electron donors results in lower FOG emission values.

(26) Moreover, it is clear from Table 1 that the combination of catalyst III and nPTES leads to the lowest FOG values at given MFR and given T.sub.R1. This can be for example illustrated by comparing CE1/RE1 (catalyst I and nPTES) or CE3/RE3 (catalyst III and DiPDMS) with CE4/RE43 (catalyst III and nPTES).

(27) Additional Examples are presented in Table 2 with the combination of catalyst III and nPTES for a series of propylene homopolymers produced at four different T.sub.R1 (50, 60, 70 and 80° C., pressure 22 bar) with a melt flow rate of 30 dg/min.

(28) TABLE-US-00002 TABLE 2 Polymerization and FOG data of propylene homopolymers of melt flow rate 30 dg/min T.sub.R1 H.sub.2/C.sub.3 FOG Exp # Catalyst External Donor ° C. mol/mol μg/g RE51 III nPTES 50 0.016 360 CE5 III nPTES 60 0.0149 280 RE52 III nPTES 70 0.008 220 RE53 III nPTES 80 0.0037 180

(29) Same observations are made from Table 2 with respect to the positive effect of higher T.sub.R1 decreasing the FOG emission value of the propylene homopolymers.

(30) The findings from these results on propylene homopolymers can be applied for heterophasic propylene copolymers as is demonstrated below.

(31) Heterophasic Propylene Copolymer Polymerization Experiments (No Pre-Polymerization)

(32) Step I)

(33) Two heterophasic propylene copolymers (Examples CE6C and RE6C) were produced by co-polymerization of propylene and ethylene using two reactors in series. In the first reactor, their respective propylene homopolymers (Examples CE6H and RE6H) were produced by varying the reaction temperature (T.sub.R1) from 65° C. (Example CE6H) to 70° C. (Example RE6H). After polymerization of the propylene homopolymer matrix phase, the powder was transported from the first to the second reactor where the polymerization of the rubber phase consisting of an ethylene-propylene copolymer was done. Materials were prepared using the catalyst system composed of catalyst III and nPTES that shows the most promising results in terms of FOG emissions for propylene homopolymers (see Tables 1 and 2). The pressure in the first reactor was 23 bar, the pressure in the second reactor was 22 bar. Table 3 provides an overview of reactor powders that were prepared in this manner. MFR R1 represents the melt flow rate of the propylene homopolymer manufactured in the first reactor, whereas MFR R2 represents the melt flow rate of the intermediate heterophasic propylene copolymer, i.e. the heterophasic propylene copolymer powder. T.sub.R1-T.sub.R2 represents the difference of operating temperatures between the first reactor and the second reactor. RC represents the amount of rubber phase based on the total weight of the heterophasic propylene copolymer and was measured by .sup.13C-NMR. The ethylene weight percentage of the ethylene-propylene rubber phase (i.e. RCC2) was set at 52 wt % for all the heterophasic propylene copolymers and was also measured by .sup.13C-NMR.

(34) TABLE-US-00003 TABLE 3 FOG data of PP homopolymers and respective intermediate heterophasic propylene copolymers (RCC2 52 wt %) MFR T.sub.R1 − MFR H.sub.2/C.sub.3 R1 R1 T.sub.R1 T.sub.R2 T.sub.R2 R2 RC FOG Exp # mol/mol dg/min ° C. ° C. ° C. dg/min wt. % μg/g CE6H 0.012  30 65 — — — — 250 CE6C 0.012  30 65 62 3 12 23 265 RE6H 0.0085 30 70 — — — — 210 RE6C 0.0085 30 70 62 8 12 23 215

(35) From Table 3, it is clear that increasing T.sub.R1 reduces FOG emissions of the intermediate heterophasic propylene copolymer, with T.sub.R2 kept constant in the present examples at 62° C. This can be observed when comparing Example RE6C and comparative Example CE6C together, both having the same composition but with the propylene homopolymer polymerized in the first reactor at a temperature of 70° C. and 65° C., respectively.

(36) Step II)

(37) For achieving high flow propylene heterophasic copolymers, these reactor powders (the intermediate heterophasic propylene copolymer powders) were melt-processed by peroxide shifting (i.e. visbreaking) to higher melt flow rates to obtain the final heterophasic propylene copolymer. This was done by feeding the powder to an extruder and adding Luperco 802PP40 as a peroxide (1,4-bis(2-tert-butylperoxypropan-2-yl)benzene, CAS Registry Number: 2781-00-2) in different concentrations. Table 4 lists details of the visbreaking experiments for reactor powders CE6C and RE6C including starting MFR (intermediate MFR) and final MFR (target MFR), the amount of peroxide in weight percentage and FOG values. Besides the peroxide, some additives common in the art were also added (0.25 weight percentage). The additive package was the same for all experiments.

(38) TABLE-US-00004 TABLE 4 FOG data of PP impact base powders (the intermediate heterophasic propylene copolymer) and the peroxide shifted products (the final heterophasic propylene copolymer) Intermediate MFR Target MFR $\frac{\mathrm{Target}\mathrm{MFR}}{\mathrm{Intermediate}\mathrm{MFR}}$ Peroxide RC FOG Exp # dg/min dg/min — wt. % wt. % μg/g CE6C 12 12 1 0 23 265 CE6C-S1 12 61 5.2 0.2 23 410 RE6C 12 12 1 0 23 215 RE6C-S1 12 58 4.8 0.19 23 340 *CE6C-S1 is peroxide shifted heterophasic copolymers from experiment CE6C, RE6C-S1 is peroxide shifted heterophasic copolymers from experiment RE6C. *intermediate MFR is the MFR of the intermediate heterophasic propylene copolymer *target MFR is the MFR of the final heterophasic propylene copolymer *shifting ratio is the target MFR divided by the intermediate MFR

(39) Table 4 shows that the visbreaking of an intermediate heterophasic propylene copolymer to higher melt flow rates to obtain the final heterophasic propylene copolymer commonly results in increased FOG values. This can be for example illustrated by comparing CE6C-S1 with CE6C, or also by comparing RE6C-S1 with RE6C.

(40) However, it is also clear from Table 4 that the positive effect of increasing T.sub.R1 during the polymerization process of the intermediate heterophasic propylene copolymer on lowering its FOG value is preserved when peroxide shifting the powder to higher melt flow rates to obtain the final heterophasic propylene copolymer. For instance, Example RE6C-S1 has lower FOG value than Example CE6C-S1, although both heterophasic propylene copolymers have the same composition and are both peroxide shifted from a melt flow 12 to about 60 dg/min; the only difference between the two examples is the temperature in the first reactor (T.sub.R1) during the polymerization process of their respective intermediate heterophasic propylene copolymer; the higher T.sub.R1, the lower the FOG value of the final heterophasic propylene copolymer.

(41) The person skilled in the art knows how to vary the MFR value of the intermediate heterophasic propylene copolymer (for example by varying the MFR of the propylene homopolymer, by varying the MFR of the rubber phase or by varying the RC). As is shown above, the MFR value of the intermediate heterophasic propylene copolymer influences the FOG values for the desired MFR of the final heterophasic propylene copolymer.

(42) As also shown by the examples above and below, the shifting ratio is preferably chosen such that it complies with the following formula:
0.0011x.sup.2−0.011x+1≤shifting ratio≤−0.0009x.sup.2+0.1963x+1

(43) wherein x stands for the melt flow rate of the final heterophasic propylene copolymer obtained after visbreaking of the intermediate heterophasic propylene copolymer, wherein the shifting ratio is the melt flow rate of the final heterophasic propylene copolymer divided by the melt flow rate of the intermediate heterophasic propylene copolymer, wherein the melt flow rates are measured in accordance with ISO1133 (230° C., 2.16 kg).

(44) Therefore, the present examples demonstrate that heterophasic propylene copolymers with decreased FOG emissions (with optionally a high flow) can be produced using the process of the invention.

(45) Heterophasic Propylene Copolymer Polymerization Experiments (with Pre-Polymerization)

(46) Step I)

(47) Two heterophasic propylene copolymers (CE7C and RE7C) were produced by co-polymerization of propylene and ethylene using two reactors in series. Materials were prepared using the catalyst system composed of catalyst III and nPTES that shows the most promising results in terms of FOG emissions for propylene homopolymers (Tables 1 and 2). The comparative example (CE7C) was obtained using the typical two-step polymerization process with the propylene homopolymer matrix phase produced in the first reactor (CE7H) at a reference T.sub.R1 of 65° C. and subsequently the ethylene-propylene copolymer produced in the second reactor at T.sub.R2 of 62° C. to obtain the intermediate heterophasic propylene copolymer (CE7C). Whereas, the example of the present invention (RE7C) was obtained including a prepolymerization stage prior to the two-step polymerization process. During the prepolymerization stage, the catalyst components were contacted with the propylene monomer at a temperature of 25° C. for 10 minutes prior to feeding into the first polymerization reactor of the series. Then, the propylene homopolymer (RE7H) was produced at a higher temperature (T.sub.R1) of 80° C. After polymerization of the propylene homopolymer matrix phase, the powder was transported from the first to the second reactor where the polymerization of the rubber phase consisting of an ethylene-propylene copolymer was done at the unchanged temperature (T.sub.R2) of 62° C. Table 5 provides an overview of reactor powders that were prepared in this manner. MFR R1 represents the melt flow rate of the propylene homopolymer manufactured in the first reactor, whereas MFR R2 represents the melt flow rate of the intermediate heterophasic propylene copolymer powder, i.e. the propylene heterophasic copolymers. T.sub.R1-T.sub.R2 represents the difference of operating temperatures between the first reactor and the second reactor. RC represents the amount of rubber phase based on the total weight of the heterophasic propylene copolymer and was measured by .sup.13C-NMR. The ethylene weight percentage of the ethylene-propylene rubber phase (i.e. RCC2) was set at 47 wt % for all the heterophasic propylene copolymers and was also measured by .sup.13C-NMR.

(48) TABLE-US-00005 TABLE 5 FOG data of PP homopolymers and respective heterophasic copolymers (RCC2 47 wt %) H.sub.2/C.sub.3 R1 MFR R1 Prepol T.sub.R1 T.sub.R2 T.sub.R1 − T.sub.R2 MFR R2 RC FOG Exp # mol/mol dg/min ° C. ° C. ° C. ° C. dg/min wt. % μg/g CE7H 0.0123 36 No 65 — — — — 260 CE7C 0.0123 36 No 65 62 3 11.5 27 275 RE7H 0.0047 36 Yes 80 — — — — 160 RE7C 0.0047 36 Yes 80 62 18 11.5 27 170

(49) From Table 5, it is clear that further increasing T.sub.R1 by using of a prepolymerization stage reduces even more FOG emissions of the propylene heterophasic copolymers, with T.sub.R2 kept constant at 62° C. This can be observed when comparing Examples CE7C and RE7C together, having the same composition but with the propylene homopolymer polymerized in the first reactor at a temperature of 65° C. with no prepolymerization and 80° C. including a prepolymerization stage, respectively. The use of prepolymerization enables to further increase T.sub.R1 while avoiding fines and lumps formation in the first reactor, but also maintaining enough residual activity of the catalyst when entering the second reactor for incorporating the target amount of ethylene-propylene copolymer phase (i.e. RC).

(50) Step II)

(51) For achieving high flow propylene heterophasic copolymers, these reactor powders (the intermediate heterophasic propylene copolymer powders) were melt-processed by peroxide shifting (i.e. visbreaking) to higher melt flow rates to obtain the final heterophasic propylene copolymer as described above. Table 6 lists details of the visbreaking experiments for reactor powders CE7C and RE7C including starting MFR (intermediate MFR) and final MFR (target MFR), the amount of peroxide in weight percentage and FOG values. Besides the peroxide, some additives common in the art were also added (0.25 weight percentage). The additive package was the same for all experiments.

(52) TABLE-US-00006 TABLE 6 FOG data of PP impact base powders (the intermediate heterophasic propylene copolymer) and the peroxide shifted products (the final heterophasic propylene copolymer) Intermediate MFR Target MFR $\frac{\mathrm{Target}\mathrm{MFR}}{\mathrm{Intermediate}\mathrm{MFR}}$ Peroxide RC FOG Exp # dg/min dg/min — wt. % wt. % μg/g CE7C 11.5 11.5 1 0 27 275 CE7C-S1 11.5 60 5.2 0.2 27 425 RE7C 11.5 11.5 1 0 27 170 RE7C-S1 11.5 61 5.3 0.21 27 305 *CE7C-S1 is peroxide shifted heterophasic copolymers from experiment CE7C, RE7C-S1 is peroxide shifted heterophasic copolymers from experiment RE7C. *intermediate MFR is the MFR of the intermediate heterophasic propylene copolymer *target MFR is the MFR of the final heterophasic propylene copolymer *shifting ratio is the target MFR divided by the intermediate MFR

(53) Table 6 shows that the visbreaking of an intermediate heterophasic propylene copolymer to higher melt flow rates to obtain the final heterophasic propylene copolymer commonly results in increased FOG values. This can be for example illustrated by comparing CE7C-S1 with CE7C, or also by comparing RE7C-S1 with RE7C.

(54) However, it is also clear from Table 6 that the positive effect of further increasing T.sub.R1, through using a prepolymerization stage prior to the two-step polymerization process of the intermediate heterophasic propylene copolymer, on lowering its FOG value is preserved when peroxide shifting the powder to higher melt flow rates to obtain the final heterophasic propylene copolymer. For instance, Example RE7C-S1 has much lower FOG value than comparative Example CE7C-S1, although both heterophasic propylene copolymers have the same composition and are both peroxide shifted from 11.5 to about 60 dg/min; the only difference between the two examples is the temperature in the first reactor (T.sub.R1) during the polymerization process of their respective intermediate heterophasic propylene copolymer; the higher T.sub.R1, the lower the FOG emissions of the final heterophasic propylene copolymer.

(55) Conclusion

(56) Therefore, the present examples demonstrate that heterophasic propylene copolymers with decreased FOG emissions (with optionally a high flow) can be produced using the process of the invention.