Heterophasic propylene copolymer

Abstract

The invention relates to a process for the preparation of a final heterophasic propylene copolymer (A) having a final melt flow rate in the range from 65 to 110 dg/min, comprising visbreaking an intermediate heterophasic propylene copolymer (A′) having an intermediate melt flow rate, which intermediate melt flow rate is lower than the final melt flow rate, to obtain the final heterophasic propylene copolymer, wherein the intermediate heterophasic propylene copolymer (A′) consists of (a) a propylene-based matrix, (b) a dispersed ethylene-α-olefin copolymer, wherein the sum of the total amount of propylene-based matrix and total amount of the dispersed ethylene-α-olefin copolymer in the intermediate heterophasic propylene copolymer is 100 wt % based on the intermediate heterophasic propylene copolymer.

Claims

1. Process for the preparation of a final heterophasic propylene copolymer having a final melt flow rate of 9 to 80 dg/min as measured according to ISO1133 at 230° C. and 2.16 kg, comprising: visbreaking an intermediate heterophasic propylene copolymer having an intermediate melt flow rate, which intermediate melt flow rate is lower than the final melt flow rate, to obtain the final heterophasic propylene copolymer, wherein the intermediate 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 prepared from 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 (b) a dispersed ethylene-α-olefin copolymer, wherein the sum of the total amount of propylene-based matrix and total amount of the dispersed ethylene-α-olefin copolymer in the intermediate heterophasic propylene copolymer is 100 wt %, based on the intermediate heterophasic propylene copolymer, wherein the dispersed ethylene α-olefin copolymer has an average rubber particle size d.sub.50 of 1.0-2.0 μm as determined by scanning electron microscopy, and wherein the intermediate heterophasic propylene copolymer has a fraction insoluble in p-xylene at 25° C. (CXI) in the range of 65 to 77 wt %, based on the intermediate heterophasic propylene copolymer, and a fraction soluble in p-xylene at 25° C. (CXS) in the range of 23 to 35 wt. % based on the intermediate heterophasic propylene copolymer, wherein the CXS has an intrinsic viscosity of at least 2.6 dl/g, wherein the sum of the total amount of CXI and total amount of CXS in the intermediate heterophasic propylene copolymer is 100 wt. %, wherein the ratio of the intrinsic viscosity of the CXS (IV-CXS) to the intrinsic viscosity of the CXI (IV-CXI) is in the range from 1.5 to 4.5 dl/g, and wherein the intrinsic viscosity is determined according to DIN EN ISO 1628-1 and 1628-3.

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

3. The process according to claim 1, wherein the intrinsic viscosity of the CXI (IV-CXI) is in the range of 0.50 to 3.5.

4. The process according to claim 1, wherein the amount of ethylene in the ethylene-α-olefin copolymer of the intermediate heterophasic propylene copolymer as measured by Fourier Transform Infrared Spectroscopy) is from 30 to 65 wt %, and/or wherein the α-olefin in the ethylene-α-olefin copolymer is propylene.

5. The process according to claim 1, wherein the intermediate heterophasic propylene copolymer used in the process of the invention has a CXS in the range from 25 to 32 wt % based on the intermediate heterophasic propylene copolymer.

6. The process according to claim 1, wherein melt flow rate of the intermediate heterophasic propylene copolymer is in the range of 3.0 to 8.0 dg/min as measured according to ISO1133 (2.16 kg/230° C.).

7. The process according to claim 1, wherein the intermediate heterophasic propylene copolymer has molecular weight distribution (Mw/Mn) in the range from 5.8 to 10.0, wherein Mw stands for the weight average molecular weight and Mn stands for the number average molecular weight are measured by SEC analysis.

8. The process according to claim 1, wherein the final melt flow rate of the final heterophasic propylene copolymer is in the range from 9 to 45 dg/min, as determined using ISO 1133 (230° C., 2.16 kg).

9. The process according to claim 1, wherein the shifting ratio, which is the ratio of the final melt flow rate to the intermediate melt flow rate is in the range from 1.5 to 20.

10. The process according to claim 1, wherein the intrinsic viscosity of the CXI (IV-CXI) is in the range of 1.0 to 2.5, wherein the amount of ethylene in the ethylene-α-olefin copolymer of the intermediate heterophasic propylene copolymer as measured by Fourier Transform Infrared Spectroscopy) is from 40 to 55 wt %, and wherein the final melt flow rate of the final heterophasic propylene copolymer is in the range from 9 to less than 40 dg/min as determined using ISO 1133 (230° C., 2.16 kg).

11. The process according to claim 10, wherein the propylene-based matrix consists of a propylene homopolymer, and wherein the α-olefin in the ethylene-α-olefin copolymer is propylene.

12. The process according to claim 1, wherein the intermediate heterophasic propylene copolymer used in the process has a CXS in the range from 25 to 32 wt % based on the intermediate heterophasic propylene copolymer, wherein melt flow rate of the intermediate heterophasic propylene copolymer is in the range of 3.0 to 8.0 dg/min as measured according to ISO1133 (2.16 kg/230° C.), wherein the intermediate heterophasic propylene copolymer has molecular weight distribution (Mw/Mn) in the range from 6.0 to 9.5, wherein Mw stands for the weight average molecular weight and Mn stands for the number average molecular weight are measured by SEC analysis, and wherein the shifting ratio, which is the ratio of the final melt flow rate to the intermediate melt flow rate is in the range from 2 to 10.

Description

(1) FIG. 1 (FIG. 1) illustrates the feeding system and the mold. The molten sample was injected through a sprue with an upper end having a diameter of 4 mm and a lower end having a diameter of 7 mm. The lower end of the sprue merges with a rectangular channel of the mold, the rectangular channel having a width of 6.5 mm and a depth of 3 mm.

(2) FIG. 2 (FIG. 2) illustrates one type of a gate system called a fan gate. After the rectangular channel having a length of 43 mm, a fan shaped part follows having a length of 25 mm. Along the length of the fan shaped part, the width changes from 6.5 mm to 30 mm and the thickness changes from 3 mm to 2 mm. After the fan shaped part, an elongated part follows having a width of 30 mm and a thickness of 3 mm.

(3) FIG. 3 (FIG. 30 illustrates another type of a gate system called a pin-point gate. The pin-point gate is identical to the fan gate of FIG. 2 except that the rectangular channel has three regions: a first region having a length of 32 mm and a width of 6.5 mm, followed by a second region having a length of 6 mm and a width of 1.2 mm, followed by a third region having a length of 5 mm and a width of 6 mm.

(4) The melt temperature during the injection was set to 240° C. and the mold set to room temperature. Three different screw speeds were used according to Table 1. Specimens having a smooth side and a textured side were manufactured.

(5) TABLE-US-00001 TABLE 1 Injection molding conditions of the tiger stripe rulers Screw speed Flow Injection Condition injection [mm/s] rate [cm.sup.3/s] time [s] Low speed 20 14.1 2.49-2.51 Medium speed 50 35.3 0.99-1.0  High speed 160 113.1 0.38-0.39

(6) After moulding, each of the specimens was visually observed for occurrence of tiger stripes on its smooth side and textured side. The quality of the surface was evaluated on a scale of 1 to 10, with 10 being the best, as described in Table 2.

(7) The average tiger stripe rating is defined as the numerical average of the individual tiger stripe ratings for each of the test specimens manufactured at low, medium and high speed, manufactured with the pin-gate and the fan-gate and measured on the smooth and on the textured surface. Hence, the average tiger stripe rating as defined herein is the average of 12 individual tiger stripe measurements.

(8) TABLE-US-00002 TABLE 2 1 very sharp transition between glossy and dull sections visible seen from any angle 2 sharp transitions between glossy and dull sections seen from any angle 3 very visible transitions between glossy and dull sections seen from any angle 4 visible transitions between glossy and dull sections seen from any angle 5 less visible transitions between glossy and dull sections seen from any angle 6 visible transitions between glossy and dull sections seen from a specific angle only 7 less visible transitions between glossy and dull sections seen from a specific angle only 8 no transitions between glossy and dull sections visible and surface appearance inhomogeneous 9 no transitions between glossy and dull sections visible and surface appearance homogeneous 10 no transitions between glossy and dull sections visible and surface is perfect

Experimental

(9) Catalyst A

(10) Catalyst A 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.

(11) Preparation of Intermediate Heterophasic Propylene Copolymers

(12) Step I)

(13) 4 heterophasic propylene copolymers (E1, E2, E3, CE4)) were produced by co-polymerization of propylene and ethylene using two reactors in series. In the first reactor (temperature 60-85° C., pressure 2.2.10.sup.1-3.0 10.sup.1 bar), the propylene homopolymer matrix phase was prepared. After polymerization, the powder was transported from the first to the second reactor (temperature 60-85° C., pressure 2.2.10.sup.1-3.0 10.sup.1 bar) 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 A and di(iso-propyl) dimethoxysilane (DiPDMS). Table 3 provides an overview of reactor powders E1, E2, E3 and CE4 that were prepared in this manner. MFR R1 (MFR.sub.R1) represents the melt flow rate of the propylene homopolymer manufactured in the first reactor. Propylene homopolymers were produced at different (H2/C3).sub.R1 molar ratios, due to the different target melt flow rates (MFR R1). (H2/C3).sub.R1 is the molar ratio of hydrogen to propylene in the gas cap of the first reactor, measured by on-line gas chromatography and adjusted to reach the target MFR R1. MFR R2 (MFR.sub.R2) represents the melt flow rate of the intermediate heterophasic propylene copolymer powder obtained after the polymerization of the rubber phase in the second reactor.

(14) CXS and CXI represent, respectively, the amount of soluble and insoluble fractions in p-xylene at 25° C. based on the total weight of the heterophasic propylene copolymer. IV-CXS and IV-CXI represent the intrinsic viscosities of the p-xylene soluble and p-xylene insoluble fractions, respectively, measured in decaline at 135° C. according to DIN EN ISO 1628-1 and -3. The IV ratio is defined as the ratio of IV-CXS to IV-CXI.

(15) M.sub.w/M.sub.n is defined as the molecular weight distirbution and is measured by SEC analysis with universal calibration. RCC2 is the ethylene weight percentage of the ethylene-propylene copolymer phase measured by FTIR spectroscopy.

(16) TABLE-US-00003 TABLE 3 Properties of intermediate heterophasic propylene copolymers MFR R1 (H2/C3).sub.R1 MFR R2 CXS IV-CXS CXI IV-CXI IV ratio M.sub.w/M.sub.n RCC2 Exp # dg/min mol/mol dg/min wt. % dl/g wt. % dl/g — — wt. % El 15.4 0.021 4.2 25.1 2.9 74.9 1.8 1.66 6.2 54.1 E2 23.5 0.028 4.8 28   2.8 72   1.6 1.75 6.3 43.6 E3 30.2 0.036 3.7 27.7 4.3 72.3 1.7 2.61 9.4 43.7 CE4  9.9  0.0175 4.4 28.3 2.1 71.7 1.8 1.20 5.4 42.3

(17) Step II)

(18) For achieving high flow propylene heterophasic copolymers, these reactor powders (the intermediate heterophasic propylene copolymer powders) were peroxide shifted (i.e. visbreaking) to higher melt flow rates to obtain the final heterophasic propylene copolymers. 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 to achieve for each reactor powders three different final melt flow rates close to values of 10, 20 and 40 dg/min. Table 4 lists details of the visbreaking experiments for the four reactor powders (E1, E2, E3 and CE4) including starting MFR (intermediate MFR), target MFR (final MFR) and the amount of peroxide in weight percentage. Besides the peroxide, some additives common in the art were also added (0.25 weight percentage based on the total weight of the heterophasic propylene copolymer). The additive package was the same for all experiments. Table 4 also includes 4 comparative commercially available heterophasic propylene copolymers: CE5 is SABIC® PP 108MF10, CE6 is Total® PPC 7810, CE7 is LyondellBasell® Hifax CA 7378 A.

(19) TABLE-US-00004 TABLE 4 MFR change Intermediate MFR Final MFR Peroxide Exp # dg/min dg/min wt. % E1-S10 4.2 9.8 0.055 E1-S20 4.2 19 0.104 E1-S40 4.2 40.7 0.22 E2-S10 4.8 9.4 0.03 E2-S20 4.8 16.1 0.07 E2-S40 4.8 40.2 0.18 E3-S10 3.7 9.4 0.035 E3-S20 3.7 24 0.09 E3-S40 3.7 40.6 0.215 CE4-S10 4.4 9.1 0.03 CE4-S20 4.4 19.8 0.096 CE4-S40 4.4 41.2 0.17 CE5 (108MF10) N/A 9.2 N/A CE6 (PPC 7810) N/A 13.5 N/A CE7 (CA7378A) N/A 12.1 N/A

(20) Intermediate Heterophasic Propylene Copolymer: Mechanical Properties

(21) Table 5 lists the material properties of the four intermediate heterophasic propylene copolymers. The three examples (E1, E2 and E3) have melt flow rate and Izod impact values at 23° C. and −20° C. similar to the comparative example CE4, whereas their flexural modulus is slightly higher which may be due to higher MFR of the PP matrix (MFR R1) and/or slightly lower C×S values.

(22) As can be seen from Table 5, the warpage is significantly reduced in the present examples versus CE4 which is believed to be a direct consequence of the isotropic morphology of the rubber domains within the propylene matrix.

(23) The average size of the rubber particles (d.sub.50) is also presented in Table 5. E1-E3 display higher d.sub.50 values than that of CE4.

(24) TABLE-US-00005 TABLE 5 Material properties of the intermediate heterophasic propylene copolymer powders Examples E1 E2 E3 CE4 MFR ISO 1133 @ 230° C. 4.2 4.8 3.7 4.4 (dg/min) d.sub.50 (μm) 1.6 1.36 1.15 0.67 Izod impact // 23° C. 69 70 69 69 (kJ/m.sup.2) Izod impact // −20° C. 8 9 8.5 6.8 (kJ/m.sup.2) Flexural modulus // 23° C. 960 855 865 845 (N/mm.sup.2) Warpage (24 hr at 23° C.) 1.1 1.1 1.05 1.18 Warpage (24 hr at 23° C. + 1.1 1.1 1.05 1.20 1 hr at 90° C.) Average tiger stripe 7.4 6.3 7.4 4.8 rating 240° C.

(25) The surface morphology of the heterophasic propylene copolymers is the key parameter controlling their surface aesthetics performance, the so-called tiger stripe performance. As seen in Table 5, Examples E1-E3 have much better surface aesthetics performance than CE4 with higher average tiger stripe ratings.

(26) Final Heterophasic Propylene Copolymer with MFR of 10 dg/min: Mechanical Properties and Tiger Stripe Rating

(27) Table 6 summarizes the material properties of the final heterophasic propylene copolymers obtained after the peroxide shifting step of the intermediate heterophasic propylene copolymer powders (E1, E2, E3 and CE4) to final MFR around 10 dg/min.

(28) TABLE-US-00006 TABLE 6 Material properties of the final heterophasic propylene copolymers after the peroxide shifting step of the intermediate heterophasic propylene copolymer powders to final MFR around 10 dg/min Examples E1-S10 E2-S10 E3-S10 CE4-S10 CE5 MFR ISO 1133 @ 9.8 9.4 9.4 9.1 9.2 230° C. (dg/min) Izod impact // 23° C. 64.8 66.1 67.1 56.4 73 (kJ/m.sup.2) Izod impact // −20° C. 7.5 7.9 8.4 5.7 5.9 (kJ/m.sup.2) Flexural modulus // 920 815 840 810 890 23° C. (N/mm.sup.2) Warpage 1.05 1.08 1.04 1.17 1.3 (24 hr at 23° C.) Warpage 1.06 1.07 1.03 1.18 1.33 (24 hr at 23° C. + 1 hr at 90° C.) Average tiger stripe 7.7 7.5 7.9 5.8 6.4 rating 240° C.

(29) As can be seen from Table 6 above, E1-S10, E2-S10, E3-S10 show that the heterophasic propylene copolymers obtainable by the process of the invention show an improved combination of good impact/modulus with an improved tiger stripe rating as well as lower warpage.

(30) Final Heterophasic Propylene Copolymer with MFR of 20 dg/min: Mechanical Properties, Tiger Stripe Rating and Paintability

(31) Table 7 summarizes the material properties of the final heterophasic propylene copolymers obtained after the peroxide shifting step of the intermediate heterophasic propylene copolymer powders (E1, E2, E3 and CE4) to final MFR around 20 dg/min.

(32) TABLE-US-00007 TABLE 7 Material properties of the final heterophasic propylene copolymers after the peroxide shifting step of the intermediate heterophasic propylene copolymer powders to final MFR around 20 dg/min Examples E1-S20 E2-S20 E3-S20 CE4-S20 CE6 CE7 MFR ISO 1133 @ 230° C. 19   16.1  20.4  19.8  13.5  12.1  (dg/min) d.sub.50 (μm)  1.42  1.12  1.03  1.05 Izod impact // 23° C. (kJ/m.sup.2) 62.9  64   62.9  49.4  60.2  37.3  Izod impact // −20° C. (kJ/m.sup.2) 7   7.4 7   5.6 8.0 8.8 Flexural modulus // 23° C. 870    800    810    780    950    1250    (N/mm.sup.2) Warpage (24hr at 23° C.)  1.01  1.02  1.01  1.12  1.04  1.08 Warpage (24hr at 23° C. + 1 hr at  1.02  1.02 1.0  1.12  1.06 1.1 90° C.) Average tiger stripe rating 240° C. 8.0 7.8 8.1 6.9 7.0 7.0 Paintability performance ++ + ++ −− − −

(33) As can be seen from Table 7 above, E1-S20, E2-S20, E3-S20 show that the heterophasic propylene copolymers obtainable by the process of the invention show an improved combination of high flow while preserving impact and flexural modulus (stiffness) with a very good tiger stripe rating, as well as a low warpage and a very good paint adhesion (paintability performance).

(34) Final Heterophasic Propylene Copolymer with MFR of 40 dg/min: Mechanical Properties and Tiger Stripe Rating

(35) Table 8 summarizes the material properties of the final heterophasic propylene copolymers obtained after the peroxide shifting step of the intermediate heterophasic propylene copolymer powders (E1, E2, E3 and CE4) to final MFR around 40 dg/min.

(36) TABLE-US-00008 TABLE 8 Material properties of the final heterophasic propylene copolymers after the peroxide shifting step of the intermediate heterophasic propylene copolymer powders to a final MFR around 40 dg/min Examples E1-S40 E2-S40 E3-S40 CE4-S40 MFR ISO 1133 @ 230° C. 40.7 40.2 40.6 41.2 (dg/min) Izod impact // 23° C. 56.5 61.21 58.4 45.5 (kJ/m.sup.2) Izod impact // −20° C. 6.9 6.4 6.3 5.3 (kJ/m.sup.2) Flexural modulus // 23° C. 820 750 760 730 (N/mm.sup.2) Warpage (24 hr at 23° C.) 0.99 1.0 0.99 1.05 Warpage (24 hr at 23° C. + 0.99 1.0 0.98 1.06 1 hr at 90° C.) Average tiger stripe 8.2 8.2 8.5 7.3 rating 240° C.

(37) As can be seen from Table 8, E1-S40, E2-S40, E3-S40 show that by process of the invention heterophasic propylene copolymers are obtained, which heterophasic propylene copolymers have a high flow in combination with a good flexural modulus (stiffness), a high impact, a very good tiger stripe rating and an excellent (around 1) warpage.

CONCLUSION

(38) To summarize the findings presented in Tables 6, 7 and 8: with the process of the invention heterophasic propylene copolymers are obtained, which heterophasic propylene copolymers have a medium to high flow and which heterophasic propylene copolymers show a good balance of impact-stiffness, a good tiger stripe rating, low warpage and excellent paint adhesion. It is also shown that the heterophasic propylene copolymers of the examples have a tough impact behavior at room temperature (Izod impact at 23° C. of above 35 kJ/m.sup.2).

(39) This makes the heterophasic propylene copolymers of the invention suitable for the production of (injection molded) articles, for example for (injection molded) automotive parts, for example for (injection molded) automotive exterior parts, such as a bumper or a body part.