Polypropylene compositions with improved stress-whitening properties

Abstract

The present invention relates to a polypropylene composition and a method for preparing the polypropylene composition. The polypropylene composition according to the present invention has improved stress whitening resistance. The present invention also relates to a battery case comprising the polypropylene composition.

Description

[0001] The present invention relates to a polypropylene composition and a method for preparing the polypropylene composition. The present invention also relates to a battery case comprising the polypropylene composition. The present invention also relates to use of the polypropylene composition in a battery case.

[0002] Polypropylene-based materials are known for use in automotive battery cases. For example, EP 3234008 B1 discloses novel injection-molded articles with improved stress-whitening properties. These articles comprise a polypropylene composition based on a heterophasic propylene copolymer and a small amount of inorganic filler. These injection-molded articles exhibit a good stiffness / impact balance and excellent stress-whitening resistance. Preferably, the article is a battery case.

[0003] There is still a need to further improve the stiffness and stress whitening resistance of materials used as battery cases.

[0004] It was an object of the present invention to provide polymer compositions having improved stress-whitening resistance and at the same time excellent stiffness.

[0005] In the context of the present invention, stiffness is quantified by flexural strength measured according to ASTM D790- 17. "Excellent stiffness" means that the polymer composition has a flexural strength of at least 30.0 MPa.

[0006] The objects of the present invention are achieved by a polymer composition comprising (A) polypropylene, (B1) a first copolymer of ethylene and an α-olefin, said first copolymer having a carbonyl group (C) of 0.891 g / cm2 as measured according to ASTM D792-13. 3 to 0.912g / cm 3 (B2) a second copolymer of ethylene and an α-olefin, the second copolymer having a density of 0.859 g / cm2 as measured according to ASTM D792-13 3 to 0.881g / cm 3 The invention relates to a polymer composition comprising a first copolymer of ethylene and an α-olefin and a second copolymer of ethylene and an α-olefin, wherein the amount of the first copolymer of ethylene and an α-olefin is 3.8 to 1.0, wherein the amount of the (A) polypropylene is 71 to 87 wt.%, based on the total amount of the polymer composition, and wherein the ratio of the amount of the second copolymer of ethylene and an α-olefin (B2) to the amount of the first copolymer of ethylene and an α-olefin (B1) is 3.8 to 1.0.

[0007] The inventors of the present invention have surprisingly found that the compositions according to the present invention have improved resistance to stress whitening while maintaining sufficient stiffness.

[0008] Polypropylene (A)

[0009] The polypropylene (A) according to this invention can be a propylene homopolymer, a propylene random copolymer or a heterophasic propylene copolymer.

[0010] Preferably, the polypropylene (A) according to this invention is a propylene homopolymer, because a propylene homopolymer is more likely to provide sufficient stiffness to the polymer composition.

[0011] Methods for producing polypropylene are known in the art. Preferably, the polypropylene of the present invention is produced in a continuous polymerization process comprising at least two reactors, more preferably, the polypropylene of the present invention is produced in a continuous polymerization process comprising at least three reactors.

[0012] Catalysts for producing polypropylene are also known in the art, such as Ziegler-Natta catalysts and metallocene catalysts. Preferably, the catalyst for producing the polypropylene of the present invention is a phthalate-free Ziegler-Natta catalyst, for example, the catalyst comprises a compound of an IUPAC Group 4 to Group 6 transition metal, a Group 2 metal compound and an internal electron donor, wherein the internal electron donor is a compound selected from substituted malonates, maleates, succinates, glutarates, cyclohexene-1,2-dicarboxylates, benzoates and derivatives and / or mixtures thereof, preferably the internal electron donor is a citraconate.

[0013] Preferably, the polymer in the polymer composition of the present invention is a polypropylene, wherein the polypropylene has a melt flow index (MFI) of 1.9 to 17.8 dg / min, preferably 2.3 to 11.2 dg / min, even more preferably 2.9 to 6.2 dg / min, measured according to ISO 1133-1:2011 at 230°C under a load of 2.16 kg.

[0014] Copolymers of ethylene and α-olefins

[0015] The composition of the present invention comprises (B1) a first copolymer of ethylene and an α-olefin and (B2) a second copolymer of ethylene and an α-olefin.

[0016] Preferably, the α-olefin comonomer in the first copolymer of (B1) ethylene and α-olefin is derived from 1-butene, 1-hexene and 1-octene, more preferably the α-olefin comonomer in the first copolymer of (B1) ethylene and α-olefin is derived from 1-octene.

[0017] Preferably, the α-olefin comonomer in (B2) the second copolymer of ethylene and α-olefin is derived from 1-butene, 1-hexene and 1-octene, more preferably the α-olefin comonomer in (B2) the second copolymer of ethylene and α-olefin is derived from 1-octene.

[0018] (B1) The first copolymer of ethylene and α-olefin has a carbonyl group (C) of 0.891 g / cm2 as measured according to ASTM D792-13. 3 to 0.912g / cm 3, preferably 0.895g / cm 3 to 0.907g / cm 3 density.

[0019] (B2) The second copolymer of ethylene and an α-olefin has a carbonyl group of 0.859 g / cm2 as measured according to ASTM D792-13. 3 to 0.881g / cm 3 , preferably 0.863g / cm 3 to 0.872g / cm 3 density.

[0020] Copolymers suitable for use in the present invention are commercially available, for example, under the trademark EXACT TM Available from Exxon Chemical Company of Houston, Texas, or under the trademark ENGAGE TM Polymers (a series of metallocene-catalyzed plastomers) are available from The Dow Chemical Company of Midland, Michigan, or under the trademark Cohere TM and Fortify TM Available from SABIC.

[0021] Copolymers can be prepared using methods known in the art, such as by using a single-site catalyst, i.e., a catalyst whose transition metal component is an organometallic compound and whose at least one ligand has a cyclopentadienyl anion structure through which this ligand is bonded and coordinated to the transition metal cation. This type of catalyst is also referred to as a "metallocene" catalyst. Metallocene catalysts are described, for example, in U.S. Patent Nos. 5,017,714 and 5,324,820. Copolymers can also be prepared using conventional heterogeneous, multisite Ziegler-Natta catalysts.

[0022] Preferably, the (B1) first copolymer of ethylene and an α-olefin has a melt flow index (MFI) of 0.5 to 2.3 dg / min, more preferably 0.7 to 1.6 dg / min, measured according to ISO 1133-1:2011 at 190°C under a load of 2.16 kg.

[0023] Preferably, (B2) the second copolymer of ethylene and an α-olefin has an MFI of 0.4 to 3.2 dg / min, more preferably 0.8 to 1.8 dg / min, measured according to ISO 1133-1:2011 at 190°C under a load of 2.16 kg.

[0024] Preferably, the ratio of the MFI of (B1) the first copolymer of ethylene and an α-olefin to the MFI of (B2) the second copolymer of ethylene and an α-olefin is from 0.5 to 2.3, preferably from 0.7 to 1.4, wherein the MFI of (B1) the first copolymer of ethylene and an α-olefin and the MFI of (B2) the second copolymer of ethylene and an α-olefin are measured according to ISO 1133-1:2011 at 190°C under a load of 2.16 kg.

[0025] The first copolymer and the second copolymer may be melt mixed with the other components by adding them as separate components. Alternatively, after melt mixing the first copolymer and the second copolymer, the first copolymer and the second copolymer may be added as one component.

[0026] Alternatively, the first copolymer and the second copolymer can be added as one component that is produced as a bimodal copolymer made by polymerizing the first (or second) copolymer and then polymerizing the second (or first) copolymer in the presence of the first (or second) copolymer. In this case, the first copolymer and the second copolymer can be polymerized in the same reactor or in different reactors. It will be understood that the molecular weight distribution of the bimodal copolymer has two peaks, corresponding to the first median and the second median at the respective stages in the polymerization.

[0027] polymer composition

[0028] The amount of (A) polypropylene in the polymer composition is 71 to 87 wt%, based on the total amount of the polymer composition.

[0029] Preferably, the total amount of (B1) the first copolymer of ethylene and an α-olefin and (B2) the second copolymer of ethylene and an α-olefin is from 15 to 29 wt%, based on the total amount of the polymer composition.

[0030] The ratio of the amount of (B2) the second copolymer of ethylene and an α-olefin to the amount of (B1) the first copolymer of ethylene and an α-olefin is 3.8 to 1.0, preferably 3.5 to 1.2, even more preferably 2.6 to 1.8.

[0031] Preferably, the polymer composition has an MFI of 2.8 to 23 g / 10 min, more preferably 3.0 to 9.2 g / 10 min, measured according to ISO 1133-1:2011 at 230°C under a load of 2.16 kg.

[0032] The polymer composition according to the present invention may further comprise additives, such as stabilizers, nucleating agents.

[0033] The polymer composition can be prepared in a conventional compounding process or by dry blending in an injection molding process. Preferably, the polymer composition is prepared in a compounding process.

[0034] In one embodiment of the present invention, the polymer composition comprises up to 3.5 wt% of an inorganic filler, wherein the inorganic filler may be talc or glass fiber.

[0035] The present invention also relates to a battery case, wherein the battery case comprises the polymer composition according to the present invention.

[0036] Preferably, the amount of the polymer composition is at least 95 wt%, more preferably at least 98 wt%, based on the total amount of the battery case.

[0037] The battery pack is the housing of a battery, wherein the preferred battery is an automotive battery, wherein the preferred battery is a lead-acid battery.

[0038] The present invention also relates to a method for preparing a battery case, the method comprising the following steps in order:

[0039] Prepare the polymer composition of the present invention by compounding;

[0040] The polymer composition obtained in the above steps is injection molded into a battery case.

[0041] The present invention also relates to the use of the polymer composition according to the invention in battery cases.

[0042] experiment

[0043] Polypropylene

[0044] PP: PP2832E1 (1080K) is a propylene homopolymer commercially available from FREP having an MFI of 3.4 g / 10 min measured according to ISO 1133-1:2011 at 230°C under a load of 2.16 kg.

[0045] Copolymers of ethylene and α-olefins

[0046] The copolymers of ethylene and α-olefin shown in Table 1 were used. The MFI shown in the table below was measured at 190° C. under a load of 2.16 kg in accordance with ISO 1133-1:2011. The density was measured in accordance with ASTM D792-13.

[0047] Table 1

[0048]

[0049] Additive Package: The additive package used in the present invention includes conventional stabilizers for polyolefins. The same type and amount of stabilizers were used in all examples.

[0050] Sample preparation

[0051] The pellets of the examples were prepared by compounding the ingredients in a Coperion ZSK 26 twin-screw extruder at the following settings:

[0052] Temperature of zones 1-9: 50℃-80℃-175℃-175℃-160℃-160℃-160℃-150℃-150℃;

[0053] Production capacity: 15kg / h;

[0054] Rotation speed: 300RPM.

[0055] The composition of the samples is shown in Table 2

[0056] Then, the pellets of Examples were supplied to an injection molding machine (FANAC S-2000i model) to prepare test specimens for the following measurements.

[0057] Measurement

[0058] Flexural strength: The flexural strength was measured according to ASTM D790-17. The measurement was carried out at 23°C.

[0059] Melt Flow Index (MFI): The MFI of the examples was measured according to ISO 1133-1:2011 using the pellets of the examples obtained after the compounding step.

[0060] Stress whitening: The samples were injection molded into plaques with the following dimensions: 250*250*2 mm. The measurements were performed at 23°C.

[0061] The stress whitening test was performed on a custom-built machine consisting of two parts: a weight release mechanism and a plate holder.

[0062] The weight release mechanism is capable of releasing a metal ball having a weight of 500 g and a diameter of 50 mm from a height H1 (in Table 2), which produces stress whitening on the test panel as a free-falling object with an initial velocity of 0.

[0063] The panel holder consists of two square metal clamps with an open space in the middle, also in the shape of a square. The clamps have external dimensions of 250 x 250 mm and internal dimensions of 230 x 230 mm. The horizontal geometric center of the outer square coincides with the horizontal geometric center of the inner square. When a panel is mounted on the panel holder, the compression between the clamps secures the panel horizontally, with the horizontal geometric center of the panel aligning with the horizontal geometric center of the clamps.

[0064] The weight release mechanism and the plate support are arranged in such a way that the drop weight impact is generated vertically on the plate surface, and the horizontal geometric center of the plate coincides with the horizontal geometric center of the impact point.

[0065] After the drop weight impact, the panels were visually inspected for the presence of whitened areas on their surfaces. Panels without any visible stress whitening received a rating of 1, and panels with visible stress whitening received a rating of 0. Ten panels were tested for each formulation, and the sum of the stress whitening ratings for each formulation was calculated.

[0066] Table 2 Sample formulation and measurement results

[0067]

[0068] *Sample destroyed after drop weight impact

[0069] In order to meet the requirements for battery cases, the stress whitening rating at H1 = 70 mm and H1 = 30 mm needs to be at least 8. It is clear from the data that only Examples EX1 and EX2 of the present invention meet this requirement.

Claims

1. A polymer composition comprising (A) polypropylene, (B1) a first copolymer of ethylene and an α-olefin, the first copolymer having a viscosity of 0.891 g / cm2 as measured according to ASTM D792-13. 3 to 0.912g / cm 3 (B2) a second copolymer of ethylene and an α-olefin, the second copolymer having a density of 0.859 g / cm 2 as measured according to ASTM D792-13 3 to 0.881g / cm 3 The density of the polypropylene (A) is 71% to 87% by weight, based on the total amount of the polymer composition, wherein the ratio of the amount of the second copolymer of ethylene and an α-olefin (B2) to the amount of the first copolymer of ethylene and an α-olefin (B1) is 3.8 to 1.

0. 2 . The polymer composition according to claim 1 , wherein the ratio of the amount of the (B2) second copolymer of ethylene and an α-olefin to the amount of the (B1) first copolymer of ethylene and an α-olefin is 3.5 to 1.

2. 3 . The polymer composition according to claim 1 , wherein the ratio of the amount of the (B2) second copolymer of ethylene and an α-olefin to the amount of the (B1) first copolymer of ethylene and an α-olefin is 2.6 to 1.

8.

4. The polymer composition according to any one of claims 1 to 3, wherein the polypropylene has a melt flow index of 1.9 to 17.8 dg / min measured according to ISO 1133-1:2011 at 230°C under a load of 2.16 kg.

5. The polymer composition according to any one of claims 1 to 3, wherein the polypropylene has a melt flow index of 2.3 to 11.2 dg / min measured according to ISO 1133-1:2011 at 230°C under a load of 2.16 kg.

6. The polymer composition according to any one of claims 1 to 3, wherein the polypropylene has a melt flow index of 2.9 to 6.2 dg / min measured according to ISO 1133-1:2011 at 230°C under a load of 2.16 kg.

7. The polymer composition according to any one of claims 1 to 3, wherein the α-olefin comonomer in (B1) the first copolymer of ethylene and an α-olefin comonomer is derived from 1-butene, 1-hexene and 1-octene.

8. The polymer composition according to any one of claims 1 to 3, wherein the α-olefin comonomer in the (B1) first copolymer of ethylene and an α-olefin comonomer is derived from 1-octene.

9. The polymer composition according to any one of claims 1 to 3, wherein the α-olefin comonomer in the (B2) second copolymer of ethylene and an α-olefin comonomer is derived from 1-butene, 1-hexene and 1-octene.

10. The polymer composition according to any one of claims 1 to 3, wherein the α-olefin comonomer in the (B2) second copolymer of ethylene and an α-olefin comonomer is derived from 1-octene.

11. The polymer composition according to any one of claims 1 to 3, wherein the (A) polypropylene is a propylene homopolymer.

12. The polymer composition according to any one of claims 1 to 3, wherein the ratio of the melt flow index of the (B1) first copolymer of ethylene and an α-olefin to the melt flow index of the (B2) second copolymer of ethylene and an α-olefin is from 0.5 to 2.3, wherein the melt flow index of the (B1) first copolymer of ethylene and an α-olefin and the melt flow index of the (B2) second copolymer of ethylene and an α-olefin are measured according to ISO 1133-1:2011 at 190°C under a load of 2.16 kg.

13. The polymer composition according to any one of claims 1 to 3, wherein the ratio of the melt flow index of the (B1) first copolymer of ethylene and an α-olefin to the melt flow index of the (B2) second copolymer of ethylene and an α-olefin is from 0.7 to 1.4, wherein the melt flow index of the (B1) first copolymer of ethylene and an α-olefin and the melt flow index of the (B2) second copolymer of ethylene and an α-olefin are measured according to ISO 1133-1:2011 at 190°C under a load of 2.16 kg.

14. The polymer composition according to any one of claims 1 to 3, wherein the (B1) first copolymer of ethylene and an α-olefin has a melt flow index of 0.5 to 2.3 dg / min measured according to ISO 1133-1:2011 at 190°C under a load of 2.16 kg.

15. The polymer composition according to any one of claims 1 to 3, wherein the (B1) first copolymer of ethylene and an α-olefin has a melt flow index of 0.7 to 1.6 dg / min measured according to ISO 1133-1:2011 at 190°C under a load of 2.16 kg.

16. The polymer composition according to any one of claims 1 to 3, wherein the (B2) second copolymer of ethylene and an α-olefin has a melt flow index of 0.4 to 3.2 dg / min measured according to ISO 1133-1:2011 at 190°C under a load of 2.16 kg.

17. The polymer composition according to any one of claims 1 to 3, wherein the (B2) second copolymer of ethylene and an α-olefin has a melt flow index of 0.8 to 1.8 dg / min measured according to ISO 1133-1:2011 at 190°C under a load of 2.16 kg.

18. The polymer composition according to any one of claims 1 to 3, wherein the polymer composition has a melt flow index of 2.8 to 23 g / 10 min measured according to ISO 1133-1:2011 at 230°C under a load of 2.16 kg.

19. The polymer composition according to any one of claims 1 to 3, wherein the polymer composition has a melt flow index of 3.0 to 9.2 g / 10 min measured according to ISO 1133-1:2011 at 230°C under a load of 2.16 kg.

20. A battery case comprising the polymer composition according to any one of claims 1 to 19.

21. A method for preparing a battery case, comprising the following steps in the following order: preparing the polymer composition according to any one of claims 1 to 19 by compounding; The polymer composition obtained from the previous steps is injection molded into a battery case.

22. Use of the polymer composition according to any one of claims 1 to 19 in a battery case.

Images