Composition comprising heterophasic propylene copolymer

Abstract

The invention relates to a composition comprising (A) a heterophasic propylene copolymer and (B) a block copolymer, 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--olefin copolymer consisting of at least 70 wt % of propylene and at most 30 wt % of -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--olefin copolymer, wherein the dispersed ethylene--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--olefin copolymer in the heterophasic propylene copolymer is 100 wt %, and wherein the block copolymer comprises a terminal block comprising styrene or alpha-methylstyrene and wherein the ratio of the melt flow rate of (A) the heterophasic propylene copolymer (MFIheterophasic) and the melt flow rate of (B) the block copolymer (MFIblock) is at most 50, preferably at most 40, at most 30, at most 25 or at most 20, wherein MFIheterophasic and MFIblock are measured in accordance with ISO 1133 using a 2.16 kg weight and at a temperature of 230 C.

Claims

1. A composition comprising (A) a heterophasic propylene copolymer and (B) a block copolymer, 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--olefin copolymer consisting of at least 90 wt % of propylene and at most 10 wt % of -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--olefin copolymer, wherein the dispersed ethylene--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--olefin copolymer in the heterophasic propylene copolymer is 100 wt %, and wherein the block copolymer comprises a terminal block comprising styrene or alpha-methylstyrene, and wherein the ratio of the melt flow rate of (A) the heterophasic propylene copolymer (MFIheterophasic) and the melt flow rate of (B) the block copolymer (MFIblock) is at most 50, wherein MFIheterophasic and MFIblock are measured in accordance with ISO 1133 using a 2.16 kg weight and at a temperature of 230 C., wherein the amount of alpha-methylstyrene and/or styrene in the block copolymer is less than 20 wt %, based on the block copolymer, wherein the block copolymer has a non-terminal block comprising ethylene and the ethylene is present in the block copolymer in an amount of 10-40 wt %, wherein the amount of the block copolymer in the composition is between 0.5-10 wt % based on the total weight of the composition, wherein the amount of inorganic filler in the composition is at most 0.5 wt %.

2. Composition according to claim 1, wherein the amount of alpha-methylstyrene and/or styrene in the block copolymer is less than 15 wt % based on the block copolymer.

3. Composition according to claim 1, wherein the amount of the block copolymer in the composition is between 1-5 wt % based on the total weight of the composition.

4. The composition according to claim 1, wherein the properties of the composition fulfil the following equation: $\begin{array}{cc}{\left(1+\frac{\mathrm{Spot}\mathrm{whiteness}\text{of}\mathrm{composition}}{\begin{array}{c}\mathrm{Spot}\mathrm{whiteness}\mathrm{of}\mathrm{heterophasic}\\ \mathrm{propylene}\mathrm{copolymer}\end{array}}\right)}^{\frac{\mathrm{haze}\mathrm{of}\mathrm{composition}}{\begin{array}{c}\mathrm{haze}\mathrm{of}\mathrm{heterophasic}\\ \mathrm{propylene}\mathrm{copolymer}\end{array}}}<2.3& \left(\mathrm{equation}1\right)\end{array}$ wherein the spot whiteness of the composition and of the heterophasic propylene copolymer are determined by creating a white spot on a test piece with dimension 65*65*3.2 mm made by injection according to ISO 37/2 by dropping a ball of 500 grams from a height of 230 mm according to PV3905, taking a photo of the white spot, calculating a spot size of the white spot in the photo, wherein the spot size is defined as the size of the area which has 99.5% of the whiteness of the photo and calculating the spot whiteness by dividing a total whiteness of the white spot by the spot size, wherein the total whiteness of the white spot is 99.5% of the whiteness of the photo; and wherein the haze of the composition and of the heterophasic propylene copolymer are determined according to ASTM D1003A.

5. The composition according to claim 1, wherein the melt flow rate of (B) the block copolymer is at least 0.5.

6. The composition according to claim 1, wherein the block copolymer is polystyrene-poly(ethylene-butylene)-polystyrene.

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

8. The composition according to according to claim 1, wherein the amount of ethylene in the ethylene--olefin copolymer of the heterophasic propylene copolymer is 10-45 wt %.

9. The composition according to claim 1, wherein the MFlheterophasic is less than 15 dg/min, wherein the MFlheterophasic is measured in accordance with ISO 1133 using a 2.16 kg weight and at a temperature of 230 C.

10. The composition according to claim, wherein the MFlheterophasic is at least 15 dg/min, wherein the MFlheterophasic is measured in accordance with ISO 1133 using a 2.16 kg weight and at a temperature of 230 C.

11. A process for the preparation of the composition according to claim 1, comprising melt mixing (A) and (B).

12. An article comprising the composition of claim 1.

13. The article according to claim 12, wherein the article is a consumer appliance.

14. The article according to claim 13, wherein the article is a housing for a household, an electrical appliance, a garden power tool, a thin wall packaging, a cap, a closure, or a container.

15. The composition according to claim 1, wherein the melt flow rate of (B) the block copolymer (MFlblock) is at most 40 dg/min.

16. The composition according to claim 1, wherein the melt flow rate of (B) the block copolymer (MFlblock) is at most 25 dg/min.

Description

EXAMPLES

(1) Heterophasic Propylene Copolymer

(2) Two grades of pellets from SABIC comprising heterophasic propylene copolymer were used: CPC1 and CPC2. Both of CPC1 and CPC2 have a density of 0.905 g/cm3. The heterophasic propylene copolymers CPC1 and CPC2 comprise a matrix phase of a propylene homopolymer and 25 wt % of a dispersed phase of ethylene-propylene copolymer (RC=25 wt %). The ethylene content in the dispersed phase (RCC2) is 20%. The ethylene content in the heterophasic propylene copolymer is 5 wt %. The MFI of CPC1 is 4 dg/min at 230 C./2.16 kg. The MFI of CPC2 is 33 dg/min at 230 C./2.16 kg.

(3) CPC1 contains 5100 ppm of additives (anti-static agents, clarifiers, antioxidants and acid scavengers).

(4) CPC2 was obtained by shifting CPC1 with 1000 ppm peroxide.

(5) Block Copolymer Comprising Styrene Block

(6) Block copolymers commercially available from Kraton were used, as summarized in Table 1.

(7) TABLE-US-00001 TABLE 1 Kraton Kraton Kraton Kraton G1641 H G1645 M G1657 M D1113 B type SEBS SEBS SEBS SIS MFI (dg/min) at 0 2.2 8.1 12.7 230 C., 2.16 Kg MFI ratio relative infinite 1.8 0.5 0.3 to CPC1 MFI ratio relative infinite 15 4.1 2.6 to CPC2 Ethylene content (wt %) 22 50 0 Styrene content (wt %) 32.3-33.7 11.5-13.5 12.3-14.3 15.1-17.3

(8) Along with the MFI of the block copolymers, the ratio of the MFIheterophasic/MFIblock is included in the table.

(9) Preparation

(10) Pellets were made by compounding a heterophasic propylene copolymer and a block copolymer as summarized in Tables 2-1 and 2-2 in a Kraus Maffei Berstorff twin screw extruder ZSK25 equipped with a shift screw at 184 RPM and a throughput of 13 kg/hour. Tables 2-1 and 2-2 summarize results where the heterophasic propylene copolymer was CPC1 and CPC2, respectively.

(11) Various properties were measured as summarized in Tables 2-1 and 2-2.

(12) TABLE-US-00002 TABLE 2-1 Sample number 1 (comp) 2 3 4 5 6 (comp) 7 Heterophasic propylene copolymer CPC1 Styrene block copolymer Kraton Kraton Kraton Kraton Kraton Kraton G1657 M G1657 M G1657 M D1113 B G1641 H G1645 M wt % in composition Sample 1 5 10 5 5 5 Optical Haze (%) 44.3 43.9 46.6 51.6 46.7 51.9 42.3 Transmittance (%) 79.6 80 77.8 74.3 78.3 80.4 81 Transparency (%) 35.3 36.1 31.2 22.7 31.6 28.5 38.7 Gloss 20 76.4 78.1 78.8 77.8 76.5 71.2 76.2 White spot size 50 41 28 25 40 130 16 (mm2) Spot whiteness 40.06 37.00 27.79 21.36 32.13 50.33 24.31 Mechanical Izod (II) 0 C. 1.7 2.38 3.95 35.3 4.63 4.38 3.81 (kJ/m.sup.2) Izod (II) 23 C. 39.09 42.43 52.8 57.39 54.02 12.12 59.95 (kJ/m.sup.2) Tensile modulus 1100.4 1068.6 1010.6 952.3 1023.8 995.3 914.9 (II) (N/mm.sup.2) MFI MFI (230 C., 4.84 4.73 5.08 5.95 4.43 3.77 4.39 2.16 kg) Outcome of 2 1.88 1.7 1.63 1.84 2.5 1.58 equation 1

(13) The effects of addition of various types of styrene block copolymers to a heterophasic propylene copolymer can be understood.

(14) Lower values of the spot size and whiteness together indicate less stress whitening. Lower value of the spot size indicates that the failure of the material is limited to a smaller area. Lower value of the whiteness indicates lower colour visibility of the failure of the material.

(15) From comparison of samples 1 (comparative experiment), 3, 5, 6 (comparative experiment) and 7, it can be understood that the addition of a block copolymer having a relatively low ratio of MFIheterophasic and MFIblock (3, 5, 7) leads to a highly improved stress whitening property and impact strength while maintaining transparency and gloss and tensile modulus to acceptable levels. The addition of a block copolymer having a high ratio of MFIheterophasic and MFIblock (6) has a largely deteriorated stress whitening property and impact strength.

(16) The addition of a block copolymer comprising a block comprising ethylene (3, 7) are more favorable in terms of stress whitening property than the addition of a block copolymer not comprising a block comprising ethylene (5). There is an optimum amount of ethylene in the block copolymer for the best whitening property, which is 10-40 wt % (7 vs 3).

(17) As can be seen from the above table, for compositions according to the invention wherein the heterophasic propylene copolymer has an MFI of at most 15 dg/min, it is preferred that the outcome of equation 1 is less than 2.3, more preferably less than 2.0 as this gives the best balance between stress whitening and haze.

(18) Comparison of samples 1, 2, 3 and 4 shows that a higher content of the block copolymer leads to a lower transparency, a better stress whitening property and a higher impact strength.

(19) TABLE-US-00003 TABLE 2-2 Sample number 8 (comp) 9 10 11 12 13 (comp) 14 Heterophasic propylene copolymer CPC2 Styrene block copolymer Kraton Kraton Kraton Kraton Kraton Kraton G1657 M G1657 M G1657 M D1113 B G1641 H G1645 M wt % in composition Sample 1 5 10 5 5 5 Optical Haze (%) 66.6 66.1 69.3 71.6 93 72.3 64.5 Transmittance (%) 80.3 80.2 76.3 74.9 73.2 82.5 80.9 Transparency (%) 13.7 14.1 7 3.3 19.8 10.2 16.4 Gloss 20 61 48.7 53.4 54.2 62.4 56.7 50.7 White spot size 224 221 178 162 202 212 204 (mm2) Spot whiteness 55.27 52.56 43.90 44.12 48.64 57.87 56.55 Mechanical Izod (II) 0 C. 2.19 2.53 3.9 5.98 3.83 3.23 3.35 (kJ/m.sup.2) Izod (II) 23 C. 5.56 6.29 10.14 42.76 8.79 6.61 10.54 (kJ/m.sup.2) Tensile modulus 1042.9 1025 965.4 890.8 987.2 943.5 913.2 (II) (N/mm.sup.2) MFI MFI (230 C., 31.45 30.99 29.06 27.84 28.75 25.87 30.32 2.16 kg) Outcome of 2 1.96 1.8 1.88 2.6 2.14 2 equation 1

(20) From comparison of samples 8 (comparative experiment), 10, 12, 13 (comparative experiment) and 14, it can be understood that the addition of a block copolymer having a relatively low ratio of MFIheterophasic and MFIblock (10, 12 and 14) leads to a highly improved stress whitening property and impact strength while maintaining gloss and tensile modulus. The addition of a block copolymer having a high ratio of MFIheterophasic and MFIblock (13) does not lead to a large improvement of the stress whitening property.

(21) The addition of a block copolymer comprising a block comprising ethylene (10, 14) are more favorable in terms of transparency than the addition of a block copolymer not comprising a block comprising ethylene (12). There is an optimum amount of ethylene in the block copolymer for the best whitening property, which is more than 40 wt % (10 vs 14).

(22) Comparison of samples 8, 9, 10, 11 shows that a higher content of the block copolymer leads to a lower transparency, a better stress whitening property and a higher impact strength.

(23) As can be seen from the above table, for compositions according to the invention wherein the heterophasic propylene copolymer has an WI of at least 15 dg/min, it is preferred that the outcome of equation 1 is less than 2.3, more preferably less than 2.2, more preferably less than 2.1, even more preferably less than 2.0 as this gives the best balance between stress whitening and haze.

(24) The properties were measured as follows:

(25) Transparency

(26) Transparency is defined as Transmission minus Haze. The determination of the Haze and Transmission values was carried out in accordance with the standard ASTM D1003A. The test specimens are small plaque 65*65*1.6 mm with hinge, injected in machine Arburg 60T/DEMAG 60T, mould: 1-1-2-110.

(27) Gloss

(28) Gloss is the amount of light reflected in a certain direction by a surface of a sample made from the composition. The gloss was determined according to ISO 2813 and DIN67530 at a measurement angle of 20. The samples used for this test are obtained by injection molding ISO 37/2 on the machine Arburg 60T, mould: 1-1-1-108, with geometry 65*65*3.2 mm

(29) Stress Whitening (Spot Size and Whitening)

(30) Stress whitening is the appearance of a white area on an object when the object is stressed by a blushing operation. The appearance of the white area indicates that there is an onset of failure of the corresponding material.

(31) The blushing on the samples was created according to PV3905, by dropping a ball of 500 grams from a height of 230 mm on a test piece with dimension 65*65*3.2 mm injected on the machine Arburg 60T, mould: 1-1-1-108, by ISO 37/2.

(32) Photos of these test pieces were taken with a SLR digital camera (Canon 6D; 100 macro lens including an extender) with fixed settings and illumination conditions such that no under or over exposure is present.

(33) Image analysis of the photos was done using a Matlab Graphical Interface (GUI) in order to determine the values of two parameters spot size and spot whiteness. Parameter spot size indicates the dimensional visibility of the white area and spot whiteness indicates the colour visibility of the white area.

(34) The spot size was determined as follows:

(35) The total whiteness of the whole photo is calculated as the sum of the whiteness of each pixel in the whole photo. The whiteness of the intrinsic material is defined as 0. Each pixel constituting the sample has a whiteness of 0-255. The spot size is defined as the size of the area which has 99.5% of the whiteness of the whole photo.

(36) The spot whiteness was determined as follows:

(37) The total whiteness of the white spot in the photo is 99.5% of the whiteness of the whole photo. The spot whiteness is calculated by dividing the total whiteness of the white spot by the spot size.

(38) Impact Strength

(39) For purpose of the present invention, impact strength was measured by Izod test according to ISO 180 4A. Samples were obtained by cutting injected plaques (ISO 37/2 on the machine Arburg 60T, mould: 1-1-1-108) into 65*12.7*3.2 mm in the parallel orientation of moulding with 45 notch, radius 0.25 mm. The test temperatures were 0 C. and 23 C.

(40) Stiffness (Tensile Modulus)

(41) For purpose of the present invention, stiffness was determined by measuring the tensile modulus according to ISO 527/1A with samples in the parallel orientation of injection moulding. The test specimens were injected on machine Arburg 60T/DEMAG 60T, mould: 1-1-1-102/122, single side injection, Dimensions: 150*10*4 mm

(42) Melt Flow Index

(43) The flow of the composition obtained was determined by measuring the melt flow index according to ISO1133 at 230 C., 2.16 Kg.