POLYPROPYLENE COMPOSITION AND PREPARATION METHOD THEREFOR

Abstract

The present invention discloses a polypropylene composition. A resin matrix is composed of copolymerized polypropylene and branched polyethylene with special parameters, such that the resin matrix has a low crystallization tendency, thereby improving spraying adhesion of a surface of the resin matrix. A polyolefin elastomer (POE) in bimodal distribution is further used to improve the appearance after molding.

Claims

1. A polypropylene composition, comprising the following components in parts by weight: 55-75 parts of copolymerized polypropylene; and 3-8 parts of branched polyethylene, wherein the copolymerized polypropylene has a weight average molecular weight of 60,000-75,000 g/mol and a molecular weight distribution index of being less than or equal to 4.0; wherein the mass percentage of ethylene propylene rubber in the copolymerized polypropylene resin is 8.5%-13.5%; wherein the branched polyethylene has a weight average molecular weight of 320,000-350,000 g/mol and a degree of branching in a range of 11.0-15.0; and wherein in the branches, the content of a methyl branch ranges from 45.0% to 55.0% based on the total number of the branches, the content of an ethyl branch ranges from 30.0% to 40.0% based on the total number of the branches, and the content of a propyl branch and branches containing four or more carbon atoms ranges from 15.0% to 25.0% based on the total number of the branches.

2. The polypropylene composition according to claim 1, further comprising 0-20 parts by weight of a copolymer, wherein the copolymer is at least one of an ethylene-1-octene copolymer with a bimodal molecular weight distribution and an ethylene-1-butene copolymer with a bimodal molecular weight distribution.

3. The polypropylene composition according to claim 2, wherein the copolymer is an ethylene-1-octene copolymer with a bimodal molecular weight distribution.

4. The polypropylene composition according to claim 1, further comprising 0-20 parts by weight of an inorganic filler.

5. The polypropylene composition according to claim 4, wherein the inorganic filler is selected from 5000-10000 mesh talcum powder.

6. The polypropylene composition according to claim 1, further comprising 0-3 parts by weight of an antioxidant.

7. A method for preparing the polypropylene composition according to claim 1, comprising: mixing the copolymerized polypropylene and the branched polyethylene uniformly based on a ratio into a mixture; and then extruding and granulating the mixture by a twin-screw extruder to provide the polypropylene composition.

8. The method of claim 7, wherein the temperature along the screws is distributed as 180° C.-210° C.-200° C.

9. The method of claim 8, wherein the rotation speed is 400-700 revolutions per minute.

10. A method for preparing the polypropylene composition according to claim 2, comprising: mixing the copolymerized polypropylene, the branched polyethylene, and the copolymer uniformly based on a ratio into a mixture; and then extruding and granulating the mixture by a twin-screw extruder to provide the polypropylene composition, wherein the temperature along the screws is distributed as 180° C.-210° C.-200° C., and the rotation speed is 400-700 revolutions per minute.

11. A method for preparing the polypropylene composition according to claim 2, comprising: mixing the copolymerized polypropylene, the branched polyethylene, the copolymer, an inorganic filler, and an antioxidant uniformly into a mixture; and then extruding and granulating the mixture by a twin-screw extruder to provide the polypropylene composition, wherein the temperature along the screws is distributed as 180° C.-210° C.-200° C., and the rotation speed is 400-700 revolutions per minute.

12. The polypropylene composition according to claim 1, wherein the molecular weight distribution index is the ratio of weight average molecular weight and number average molecular weight, M.sub.w/M.sub.n.

13. The polypropylene composition according to claim 3, wherein the ethylene-1-octene copolymer with a bimodal molecular weight distribution has peaks in a weight average molecular weight range of 60,000-80,000 and in a weight average molecular weight range of 150,000-170,000, respectively.

Description

DESCRIPTION OF EMBODIMENTS

[0028] The present invention is described in detail below with reference to specific embodiments. The following embodiments help a person skilled in the art to further understand the present invention, but do not limit the present invention in any way. It should be noted that for a person of ordinary skill in the art, several variations and improvements can be further made without departing from the conception of the present invention, and shall fall within the protection scope of the present invention.

[0029] Raw materials used in the present invention are as follows:

[0030] polypropylene A: copolymerized polypropylene, with a weight average molecular weight of about 67,000-70,000 g/mol and a molecular weight distribution index of 3.5, where the mass percentage of ethylene propylene rubber in the copolymerized polypropylene resin is 9.5%;

[0031] polypropylene B: copolymerized polypropylene, with a weight average molecular weight of about 70,000-73,000 g/mol and a molecular weight distribution index of 4.0, where the mass percentage of ethylene propylene rubber in the copolymerized polypropylene resin is 10.2%;

[0032] polypropylene C: copolymerized polypropylene, with a weight average molecular weight of about 78,000-80,000 g/mol and a molecular weight distribution index of 4.0, where the mass percentage of ethylene propylene rubber in the copolymerized polypropylene resin is 18.6%;

[0033] polypropylene D: copolymerized polypropylene, with a weight average molecular weight of about 76,000-79,000 g/mol and a molecular weight distribution index of 4.9, where the mass percentage of ethylene propylene rubber in the copolymerized polypropylene resin is 13.4%;

[0034] polypropylene E: homo-polypropylene, with a weight average molecular weight of about 72,000 g/mol and a molecular weight distribution index of 3.5;

[0035] polypropylene F: copolymerized polypropylene, with a weight average molecular weight of about 90,000 g/mol and a molecular weight distribution index of 5.6, where the mass percentage of ethylene propylene rubber in the copolymerized polypropylene resin is 7.5%;

[0036] polyethylene A: with a weight average molecular weight of about 325,000-335,000 g/mol and a degree of branching of 11.5, where in the branches, the content of a methyl branch is 50.5% based on the total number of the branches, the content of an ethyl branch is 31.5% based on the total number of the branches, and the content of a propyl branch and branches containing four or more carbon atoms is 18.0% based on the total number of the branches;

[0037] polyethylene B: with a weight average molecular weight of about 340,000-350,000 g/mol and a degree of branching of 14.0, where in the branches, the content of a methyl branch is 46.0% based on the total number of the branches, the content of an ethyl branch is 34.5% based on the total number of the branches, and the content of a propyl branch and branches containing four or more carbon atoms is 19.5% based on the total number of the branches;

[0038] polyethylene C: with a weight average molecular weight of about 270,000-290,000 g/mol and a degree of branching of 10.0, where in the branches, the content of a methyl branch is 68.5% based on the total number of the branches, the content of an ethyl branch is 25.5% based on the total number of the branches, and the content of a propyl branch and branches containing four or more carbon atoms is 6.0% based on the total number of the branches;

[0039] polyethylene D: linear polyethylene, with a weight average molecular weight of about 260,000-280,000 g/mol;

[0040] polyethylene E: high density polyethylene, with a weight average molecular weight of about 350,000-370,000 g/mol;

[0041] ethylene-1-octene copolymer A: with a bimodal molecular weight distribution and a weight average molecular weight of 120,000-130,000 (with peak 1 having a weight average molecular weight of 70,000-71,000 and a peak area percentage of 39.5%, and peak 2 having a weight average molecular weight of 160,000-161,000 and a peak area percentage of 53.5%);

[0042] ethylene-1-octene copolymer B: with a monomodal molecular weight distribution and a weight average molecular weight of 96,000-106,000 (with peak 1 having a weight average molecular weight of 97,000-99,000 and a peak area percentage of 93.5%);

[0043] an ethylene-1-butene copolymer: with a bimodal molecular weight distribution and a weight average molecular weight of about 110,000-125,000 (with peak 1 having a weight average molecular weight of 73,000-75,000 and a peak area percentage of 40.5%, and peak 2 having a weight average molecular weight of 157,000-160,000 and a peak area percentage of 52.5%);

[0044] talcum powder: 8,000 mesh; and

[0045] antioxidant 1010.

[0046] Method for preparing each polypropylene composition in the embodiments and the comparative examples: Components were uniformly mixed based on the ratio and then extruded and granulated by a twin-screw extruder to obtain the polypropylene composition, where the temperature along the screws were distributed as 180° C.-210° C.-200° C., and the rotation speed is 600 revolutions per minute.

[0047] Square plate obtained by injection molding: a 100*100*3 mm square plate mold, used for a grid scratch test, a diesel fuel resistance test, and an antifreeze resistance test.

[0048] An Archimedean ring obtained by injection molding: with a length of 1000 mm, a width of 50 mm, and a thickness of 2 mm, used for a flow mark test.

[0049] Injection molding machine model: Borche BS320-III. Injection molding condition: injection molding temperature of 200° C. in an entire region, injection pressure of 70% in the entire region, holding pressure of 70% in the entire region, and cooling time of 8 seconds.

[0050] A paint spraying process was provided by Shanghai Fanuc Robot Co., Ltd.

[0051] The following tests were performed after injection molding and paint spraying.

[0052] Method for testing each property:

[0053] (1) Grid scratch test: Operation was performed based on ISO2409. A grid-scribing knife was selected based on a thickness of a coating and used for scribing to a base material, and an adhesive tape (recommended 3M-898#adhesive tape, Teasa-4657 or an adhesive tape with similar property as the foregoing two adhesive tapes) was used for pasting. To ensure good contact with the coating, the adhesive tape was rubbed heavily and evenly with fingertips and then kept for 5 min, maintained at a 60° tearing angle with the surface of a test sample, and peeled off manually within 1 second. The peeling of the coating was observed. Generally, the coating of vehicle paint has a thickness of 60-120 μm, a distance between knife marks is 2 mm, and there are six knife marks.

[0054] (2) Flow mark test: Positions of flow marks were evaluated. Length distances correspond to where the flow marks start to be visually observable on Archimedean ring samples after injection molding. There were at least 3 testers. A mathematical average of the data was taken, the result of which has been rounded to the nearest integer. If there was no flow mark seen with naked eyes, “No flow mark” was marked.

[0055] (3) Diesel fuel resistance test: Test sample pieces were placed in diesel fuel at 23±2° C. for impregnation. After impregnation for 0.5 hour, the test sample pieces were taken out and placed in air at 23±2° C. for storage for 24 hours, and then the test sample pieces were wiped clean of medium with a cleaning cloth impregnated with water (or an industrial dedusting agent, or a cleaning solution) and cleaning gasoline, and then evaluation was performed.

[0056] (4) Antifreeze resistance test: Filter paper was impregnated with antifreeze and applied to outer surfaces of samples, and surface changes of the products were observed after 1 hour.

TABLE-US-00001 TABLE 1 Polypropylene composition formulas (parts by weight) and test results of various properties in Embodiments Em- Em- Em- Em- Em- Em- Em- bodi- bodi- bodi- bodi- bodi- bodi- bodi- ment ment ment ment ment ment ment 1 2 3 4 5 6 7 Polypropylene A 70 70 70 Polypropylene B 70 70 70 70 Polyethylene A 3 5 5 5 5 Polyethylene B 8 8 Ethylene-1-octene 15 10 copolymer A Ethylene-1-octene 15 copolymer B Ethylene-1-butene 15 copolymer Talc 20 Antioxidant 1010 0.4 0.4 0.4 0.4 0.4 0.4 0.4 Grid test paint 100 100 100 100 100 100 100 retention rate (%) Adhesion (N/m) 805 820 826 876 855 832 882 after the diesel fuel resistance test Adhesion (N/m) 830 846 851 898 883 861 913 after the antifreeze resistance test Positions of flow No No No No 145 No No marks (mm) flow flow flow flow flow flow mark mark mark mark mark mark

[0057] It can be learned from Embodiment 4 or 5 that the ethylene-1-octene copolymer with a bimodal molecular weight distribution improved flow marks significantly better than the ethylene-1-octene copolymer with a monomodal molecular weight distribution.

[0058] It can be learned from Embodiment 4 or 6 that the ethylene-1-octene copolymer with a bimodal molecular weight distribution is preferred.

TABLE-US-00002 TABLE 2 Polypropylene composition formulas (parts by weight) and test results of various properties in Comparative Examples 1 to 4 Comparative Comparative Comparative Comparative Example 1 Example 2 Example 3 Example 4 Polypropylene C 70 Polypropylene D 70 Polypropylene E 70 Polypropylene F 70 Polyethylene A 3 3 3 3 Antioxidant 1010 0.4 0.4 0.4 0.4 Grid test paint 85.5 84.2 66.3 82.3 retention rate (%) Adhesion (N/m) 725 721 523 689 after the diesel fuel resistance test Adhesion (N/m) 765 748 562 732 after the antifreeze resistance test Positions of 180 204 260 195 flow marks (mm)

[0059] It can be learned from Comparative Examples 1 to 4 that it is difficult to reduce the crystallinity of the blended resin matrix if the molecular weight distribution index of the polypropylene is greater than 4.0 or the content of the ethylene propylene rubber is excessively high or excessively low.

TABLE-US-00003 TABLE 3 Polypropylene composition formulas (parts by weight) and test results of various performance in Comparative Examples 5 to 7 Comparative Comparative Comparative Example 5 Example 6 Example 7 Polypropylene A 70 70 70 Polyethylene C 3 Polyethylene D 3 Polyethylene E 3 Antioxidant 1010 0.4 0.4 0.4 Grid test paint 92.5 89.5 82.3 retention rate (%) Adhesion (N/m) 754 732 634 after the diesel fuel resistance test Adhesion (N/m) 782 753 652 after the antifreeze resistance test Positions of flow 285 265 125 marks (mm)

[0060] It can be learned from Comparative Example 5 that when the degree of branching is low and the content of branches with four or more carbon atoms is relatively low, the effect of reducing the crystallinity of the polypropylene resin matrix cannot be achieved.

[0061] It can be learned from Comparative Example 6 or 7 that linear polyethylene and high-density polyethylene cannot reduce the crystallinity of the polypropylene resin matrix as well.