Polypropylene composition as well as preparation method and application thereof

Abstract

The invention relates to a polypropylene composition as well as a preparation method and application thereof. The polypropylene composition comprises the following components in parts by weight: 58-86 parts of polypropylene, 5-17 parts of conductive carbon black, 3-9 parts of multiwalled carbon nanotubes and 0.5-2 parts of an antioxidant. The surface of the multi-walled carbon nanotube is modified with carboxyl; the mass ratio of the conductive carbon black to the multi-walled carbon nanotubes is (1.5-3): 1. According to the invention, the polypropylene is used as a resin matrix and added into the multi-walled carbon nanotube with the surface modified with carboxyl, and the mass ratio of the conductive carbon black to the multi-walled carbon nanotube is controlled within a specific range, so that the prepared polypropylene composition not only has high electromagnetic shielding effectiveness, but also has high tensile strength retention rate after thermal aging treatment, and the electromagnetic shielding performance of the polypropylene composition is improved. And the thin-wall injection molding requirement can be met.

Description

Technical Field

[0001] This application relates to the field of polymer materials technology, and in particular to a polypropylene composition, its preparation method, and its application. Background Technology

[0002] With the increasing integration of integrated circuits within modern electronic devices (such as mobile phones, computers, and 5G high-frequency equipment), the requirements for electromagnetic shielding technology are becoming increasingly stringent. If the casing material lacks shielding capabilities, signals within the device will interfere with each other, leading to performance degradation or even failure. Furthermore, electromagnetic radiation from the external environment (such as high-voltage power lines and communication base stations) may penetrate the device casing and interfere with internal precision circuits. Polypropylene (PP), due to its lightweight and chemical resistance, is widely used in electronic device casings, automotive parts, and other fields.

[0003] Traditionally, adding 10% or more conductive carbon black (CB) is required to impart conductive / electromagnetic shielding properties to PP. However, a high proportion of CB leads to the following problems: Modern electronic devices often generate heat during use, and CB, due to its high specific surface area, adsorbs antioxidants, which can significantly reduce the thermal aging performance of polypropylene and severely affect its service life. On the other hand, in thin-walled flow channels, excessive addition of conductive carbon black can increase the thermal conductivity of the melt and accelerate the cooling rate of the melt near the flow channel wall, thus easily forming a thick and hard laminar "skin". There will be a sudden change in the velocity gradient between the "skin" and the core melt that is still flowing in the middle. When the two melt flows meet at the confluence (such as at the flow channel bifurcation or mandrel), obvious flow lines and boundaries will be left on the surface, resulting in a tiger-skin pattern.

[0004] A Chinese patent describes an electromagnetic shielding polypropylene foam material and its preparation method. By injecting a gaseous foaming agent into the polypropylene material, foam cells are formed in the material, thereby improving the electromagnetic shielding performance of the resulting polypropylene foam material. However, this technology requires the addition of an extra foaming agent during the injection molding process, making the processing technology complex. Furthermore, it does not address the thermal aging performance and thin-wall injection molding performance.

[0005] Therefore, there is an urgent need to find a polypropylene composite material that can balance electromagnetic shielding effectiveness and thermal aging performance, as well as prevent the tiger-skin pattern from appearing during thin-wall injection molding. Summary of the Invention

[0006] The primary objective of this invention is to overcome the problem that existing polypropylene composite materials cannot simultaneously achieve electromagnetic shielding effectiveness, thermal aging performance, and the tiger-skin pattern that occurs during thin-wall injection molding, and to provide a polypropylene composition.

[0007] A further object of the present invention is to provide a method for preparing the above-described polypropylene composition.

[0008] Another object of the present invention is to provide the use of the above-described polypropylene composition in the manufacture of electronic device housings or automotive parts.

[0009] Another object of the present invention is to provide a polypropylene part.

[0010] The above-mentioned objective of the present invention is achieved through the following technical solution: This invention protects a polypropylene composition comprising the following components in parts by weight: 58-86 parts polypropylene, 5-17 parts conductive carbon black, 3-9 parts multi-walled carbon nanotubes, and 0.5-2 parts antioxidant. The surface of the multi-walled carbon nanotubes is modified with carboxyl groups; The mass ratio of the conductive carbon black to the multi-walled carbon nanotubes is (1.5~3):1.

[0011] The inventors of this invention have discovered that in order to meet the requirements of high electromagnetic shielding effectiveness, a large amount of conductive carbon black is usually required. However, when the amount of conductive carbon black is high, the tensile strength of the polypropylene composition after heat aging treatment will decrease significantly and tiger-skin pattern will appear during thin-wall injection molding.

[0012] The inventors of this invention further discovered that by using polypropylene as a resin matrix and adding carboxyl-modified multi-walled carbon nanotubes, and by controlling the mass ratio of conductive carbon black to multi-walled carbon nanotubes within a specific range, the resulting polypropylene composition not only has high electromagnetic shielding performance, but also has a high tensile strength retention rate after heat aging treatment, and can also meet the requirements of thin-walled injection molding.

[0013] The applicant speculates that the principle is as follows: controlling the mass ratio of conductive carbon black to multi-walled carbon nanotubes allows the conductive carbon black to be uniformly filled between the multi-walled carbon nanotubes with carboxyl groups on the surface. This not only helps to form a stable conductive network, thus giving the polypropylene composition high electromagnetic shielding performance, but also the carboxyl groups on the surface of the multi-walled carbon nanotubes can not only increase the glass transition temperature of the polypropylene composition and delay the diffusion of heat and oxygen, resulting in a high tensile strength retention rate after heat aging treatment, but also enhance the interfacial bonding between the components, thereby avoiding the tiger-skin pattern phenomenon during thin-wall injection molding.

[0014] In this invention, the amount of polypropylene resin used can be 58, 60, 62, 65, 68, 70, 72, 75, 78, 80, 82, 85, or 86 parts by weight, or any two of the above values. The amount of conductive carbon black used can be 5, 6, 7, 9, 10, 11.25, 13, 15, or 17 parts by weight, or any two of the above values. The amount of multi-walled carbon nanotubes used can be 3, 3.75, 5, 6, 8, or 9 parts by weight, or any two of the above values. The amount of antioxidant used can be 0.5, 0.6, 0.8, 1, 1.2, 1.5, 1.8, or 2 parts by weight, or any two of the above values. The mass ratio of conductive carbon black to multi-walled carbon nanotubes can be 1.5:1, 1.8:1, 2:1, 2.5:1, or 3:1, or any two of the above values.

[0015] Preferably, the polypropylene composition comprises the following components in parts by weight: 60-85 parts polypropylene, 6-17 parts conductive carbon black, 3-8 parts multi-walled carbon nanotubes, and 0.5-2 parts antioxidant.

[0016] Preferably, the mass ratio of conductive carbon black to multi-walled carbon nanotubes is (1.5~2):1. Controlling the mass ratio of conductive carbon black to multi-walled carbon nanotubes within this range results in a higher retention rate of tensile strength after thermal aging of the polypropylene composition.

[0017] Preferably, the mass ratio of conductive carbon black to multi-walled carbon nanotubes is (2~3):1. Controlling the mass ratio of conductive carbon black to multi-walled carbon nanotubes within this range results in higher electromagnetic shielding effectiveness for the polypropylene composition.

[0018] In this invention, polypropylene is used as the main resin, and its content accounts for more than 65 wt% of the polypropylene composition.

[0019] Preferably, the melt flow rate of the polypropylene at 230 °C and 2.16 kg is 5~30 g / 10 min.

[0020] In this invention, the melt flow rate of the polypropylene can be measured according to GB / T 3682-2000.

[0021] Preferably, the polypropylene is at least one of homopolymer polypropylene or copolymer polypropylene.

[0022] More preferably, the copolymer polypropylene is at least one of random copolymer polypropylene or block copolymer polypropylene.

[0023] Preferably, the conductive carbon black has an oil absorption value of 150~500 ml / 100 g and a specific surface area of ​​200~1400 m². 2 / g.

[0024] More preferably, the conductive carbon black has an oil absorption value of 192~450 ml / 100 g.

[0025] More preferably, the oil absorption value of the conductive carbon black is 192~420 ml / 100 g. Controlling the oil absorption value of the conductive carbon black within this range results in higher electromagnetic shielding effectiveness and better retention of tensile strength after thermal aging in the polypropylene composition.

[0026] In this invention, the oil absorption value of the conductive carbon black can be measured according to GB / T3780.2-2017.

[0027] Preferably, the specific surface area of ​​the multi-walled carbon nanotubes is 180~350 m². 2 / g.

[0028] In this invention, the specific surface area of ​​the conductive carbon black and multi-walled carbon nanotubes can be measured according to GB / T 19587-2004.

[0029] Preferably, the carboxyl content in the multi-walled carbon nanotubes is ≥0.5 mmol / g.

[0030] More preferably, the carboxyl content in the multi-walled carbon nanotubes is 0.52~1.05 mmol / g.

[0031] More preferably, the carboxyl content in the multi-walled carbon nanotubes is 0.52~0.8 mmol / g. Controlling the carboxyl content in the multi-walled carbon nanotubes within this range results in higher electromagnetic shielding effectiveness and better retention of tensile strength after thermal aging in the polypropylene composition.

[0032] In this invention, the carboxyl group content in the multi-walled carbon nanotubes can be determined by acid-base titration.

[0033] Preferably, the combined mass of the conductive carbon black and the multi-walled carbon nanotubes accounts for 8-30% of the total mass of the polypropylene composition.

[0034] More preferably, the combined mass of the conductive carbon black and the multi-walled carbon nanotubes accounts for 9-28% of the total mass of the polypropylene composition.

[0035] More preferably, the sum of the mass of the conductive carbon black and the multi-walled carbon nanotubes accounts for 15-19% of the total mass of the polypropylene composition. Controlling the sum of the mass of the conductive carbon black and the multi-walled carbon nanotubes within this range results in higher electromagnetic shielding effectiveness and better retention of tensile strength after thermal aging in the polypropylene composition.

[0036] In this application, the multi-walled carbon nanotubes with carboxylic acid surface modification can be obtained commercially or introduced with carboxyl groups on the surface of multi-walled carbon nanotubes by conventional self-made methods in the art, such as introducing carboxyl groups by chemical oxidation.

[0037] Specifically, in one embodiment, oxidizing acid can be used to oxidize multi-walled carbon nanotubes to obtain multi-walled carbon nanotubes with carboxyl groups modified on the surface.

[0038] Preferably, the oxidation process is as follows: multi-walled carbon nanotubes are refluxed in an oxidizing acid at 60~120 °C for 2~6 h.

[0039] More preferably, the oxidizing acid includes, but is not limited to, concentrated nitric acid.

[0040] More preferably, the oxidizing acid has a mass fraction of 62-68%.

[0041] Preferably, the aspect ratio of the multi-walled carbon nanotube is ≥150.

[0042] Preferably, the average diameter of the cross-section of the multi-walled carbon nanotube is 8~30 nm.

[0043] Preferably, the average length and average diameter of the cross-section of the multi-walled carbon nanotubes are measured according to GB / T24491-2009.

[0044] Preferably, the antioxidant is at least one of a primary antioxidant or a secondary antioxidant.

[0045] More preferably, the antioxidant comprises a primary antioxidant and a secondary antioxidant in a mass ratio of 1:(0.8~1.2).

[0046] More preferably, the primary antioxidant is a hindered phenolic antioxidant.

[0047] More preferably, the hindered phenolic antioxidant is at least one of antioxidant 1010, antioxidant 1024, or antioxidant 1076.

[0048] More preferably, the auxiliary antioxidant is a phosphite antioxidant.

[0049] More preferably, the phosphite antioxidant is at least one of antioxidant 126, antioxidant Ultranox 626, or antioxidant ADK STAB PEP24.

[0050] Preferably, the polypropylene composition further includes the following components in parts by weight: 0.1 to 2 parts of coupling agent and 0 to 5 parts of other additives.

[0051] More preferably, the polypropylene composition further includes the following components in parts by weight: 0.3 to 1.5 parts of coupling agent and 0 to 3 parts of other additives.

[0052] More preferably, the other additives are dispersants.

[0053] More preferably, the coupling agent is a silane coupling agent, including but not limited to at least one of γ-aminopropyltriethoxysilane or γ-(methacryloyloxy)propyltrimethoxysilane.

[0054] More preferably, the dispersant is at least one of calcium stearate, aluminum stearate, magnesium stearate, or zinc stearate.

[0055] The present invention protects a method for preparing the above-mentioned polypropylene composition, comprising the following steps: weighing and mixing each component according to the formula, performing melt blending, and extruding and granulating to obtain the polypropylene composition.

[0056] Preferably, the melt extrusion is carried out in an extruder.

[0057] More preferably, the extruder is a twin-screw extruder.

[0058] More preferably, the screw speed of the extruder is 300~500 rpm, the length-to-diameter ratio is (36~48):1, and the temperature is 200~240 ℃.

[0059] The present invention also protects the use of the above-described polypropylene composition in the manufacture of electronic device housings or automotive parts.

[0060] This invention protects a polypropylene part prepared from the aforementioned polypropylene composition.

[0061] Preferably, the polypropylene component is at least one of an electronic device housing or an automotive part.

[0062] Compared with the prior art, the beneficial effects of the present invention are: This invention uses polypropylene as a resin matrix and adds carboxyl-modified multi-walled carbon nanotubes to the matrix. The mass ratio of conductive carbon black to multi-walled carbon nanotubes is controlled within a specific range. The resulting polypropylene composition not only has high electromagnetic shielding performance, but also has high tensile strength retention after heat aging treatment, and can also meet the appearance requirements of thin-walled injection molding parts. Detailed Implementation

[0063] To more clearly and completely describe the technical solution of the present invention, the present invention will be further described in detail below through specific embodiments. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention. Various changes can be made within the scope of the claims of the present invention.

[0064] The reagents used in the various embodiments and comparative examples of this invention are described below: Polypropylene 1#: Sinopec, K9928, melt flow rate at 230 ℃ and 2.16 kg is 28.3 g / 10min; Polypropylene #2: CNOOC Shell, HP500N, melt flow rate at 230 ℃ and 2.16 kg is 12 g / 10min; Conductive Carbon Black #1: Cabot (USA), Vulcan XC72R, oil absorption value 192 ml / 100 g, specific surface area 254 m² 2 / g; Conductive carbon black #2: Orion (Germany), Printex XE2B, oil absorption value 420 ml / 100 g, specific surface area 1000 m² 2 / g; Conductive Carbon Black #3: Lion Corporation, Japan, Ketjenbla EC-600JD, oil absorption value 450 ml / 100 g, specific surface area 1300 m² 2 / g; Multi-walled carbon nanotubes A#: Nanocyl (Belgium), NC7000, specific surface area 280 m² 2 / g, with an average cross-sectional diameter of 9.5 nm and an aspect ratio of 158; Multi-walled carbon nanotubes B#: Aladdin, CAS No.: 308068-56-6, specific surface area 350 m² 2 / g, with an average cross-sectional diameter of 15 nm and an aspect ratio of 5333; Multi-walled carbon nanotubes 1#: self-made, the preparation process is as follows: multi-walled carbon nanotubes A# were refluxed in concentrated nitric acid with a mass fraction of 65% at 80 ℃ for 3 h; the carboxyl content of multi-walled carbon nanotubes 1# was 0.52 mmol / g; Multi-walled carbon nanotubes 2#: self-made, the preparation process of which differs from that of multi-walled carbon nanotubes 1# is: reflux time of 4 h; carboxyl content of multi-walled carbon nanotubes 2# is 0.80 mmol / g; Multi-walled carbon nanotubes #3: self-made, the preparation process of which differs from that of multi-walled carbon nanotubes #1 is: reflux time of 6 h; carboxyl content of multi-walled carbon nanotubes #3 is 1.05 mmol / g; Multi-walled carbon nanotube 4#: self-made, the preparation process of which differs from that of multi-walled carbon nanotube 1# is that multi-walled carbon nanotube A# is replaced with multi-walled carbon nanotube B#; the carboxyl content of multi-walled carbon nanotube 4# is 1.10 mmol / g; Carbon fiber: Short-cut carbon fiber, Nantong Fuyuan New Material Technology Co., Ltd., FUY-120, length 3 mm, average diameter of cross section 7 μm; Antioxidant 1#: Main antioxidant, hindered phenolic antioxidant, antioxidant 1010, Shandong Sanfeng; Antioxidant 2#: Co-antioxidant, phosphite antioxidant, antioxidant 126, BASF; Coupling agent: γ-(methacryloyloxy)propyltrimethoxysilane, commercially available; Other additives #1: Dispersant, calcium stearate, commercially available; Unless otherwise specified, all components (e.g., other additives 1#) used in the parallel examples and comparative examples are the same commercially available products.

[0065] The polypropylene compositions of the embodiments and comparative examples of the present invention were prepared by the following process: Weigh each component according to the formula, then feed it into the main feed port of a twin-screw extruder, melt-blend, and extrude and granulate to obtain a polypropylene composition.

[0066] The twin-screw extruder has the following temperature zones: Zone 1: 200℃, Zone 2: 200℃, Zone 3: 240℃, Zone 4: 240℃, Zone 5: 240℃, Zone 6: 240℃, Zone 7: 220℃, Zone 8: 220℃, Zone 9: 220℃, and Zone 10: 240℃. The twin-screw extruder has a screw speed of 300 rpm and a screw length-to-diameter ratio of 40:1.

[0067] The performance testing methods and standards for the polypropylene compositions of the various embodiments and comparative examples of the present invention are as follows: (1) Electromagnetic shielding effectiveness: Tested according to GB / T 30142-2013 standard. In the frequency range of 30 MHz to 3 GHz, the flange coaxial device method was used. The measurement conditions were: 23 ℃, relative humidity 60%, atmospheric pressure 100 kPa. The measuring equipment was: flange coaxial device, frequency range of 30 MHz to 3 GHz, measurement frequency point was 1 GHz, the thickness of the test sample was ≤10 mm, and the measurement method was the signal generator / spectrum analyzer measurement method.

[0068] (2) Tensile strength retention rate after heat aging: The polypropylene composition was divided into two groups, A and B. The initial tensile strength of group A was tested according to GB / T1040-2018, and group B was aged according to the hot air aging method in GB / T 18244-2000. The aging conditions were: 150 ℃, 1000 hours, average wind speed 0.5 m / s, air exchange rate 20 times / h, and the volume of the working chamber was 0.1 m³. 3 After being removed, the sample was equilibrated at 23 ℃±2 ℃ for 24 hours. Then, the tensile strength after heat aging was tested according to GB / T1040-2018, and the tensile strength retention rate after heat aging was calculated. The tensile strength retention rate is calculated as follows: (tensile strength after heat aging / initial tensile strength) × 100%.

[0069] (3) Thin-wall injection molding performance: The core difficulty of thin-wall injection molding lies in the rapid solidification of the melt in the extremely thin runner. When the melt comes into contact with the cold mold wall during flow, it will instantly form a solidified layer. Therefore, the performance of thin-wall injection molding can be judged by the starting position of the tiger stripe pattern. Set the injection temperature to 220 ℃, the mold temperature to 40 ℃, and use a spiral mold (total mold length 1000mm). Observe the starting position of the tiger stripe pattern on the mold. If the starting position of the tiger stripe pattern is ≥2 / 3 of the mold length, it is recorded as "qualified". Otherwise, it is recorded as "unqualified".

[0070] Examples 1-13 Examples 1-13 provide a series of polypropylene compositions, the weight parts of each component in which are shown in Table 1.

[0071] Table 1 Formulations of Examples 1-13

[0072] Comparative Examples 1-6 Comparative Examples 1-6 provide a series of polypropylene compositions, the weight parts of each component in the formulation are shown in Table 2.

[0073] Table 2 Formulations of Comparative Examples 1-6

[0074] The performance test results of the polypropylene compositions of each embodiment and comparative example according to the methods mentioned above are shown in Table 3.

[0075] Table 3 Performance test results of the polypropylene compositions in each example and comparative example

[0076] As shown in Table 3, the polypropylene compositions of Examples 1-13 have an electromagnetic shielding effectiveness of over 38 dB, a tensile strength retention rate of over 82% after heat aging, and pass the thin-wall injection molding requirements. This indicates that the polypropylene compositions of the present invention not only have high electromagnetic shielding effectiveness, but also have a high tensile strength retention rate after heat aging treatment, and can also meet the requirements for thin-wall injection molding.

[0077] Comparative Example 1, without the addition of multi-walled carbon nanotubes, resulted in a polypropylene composition with low electromagnetic shielding effectiveness, low tensile strength retention after heat aging treatment, and unsatisfactory thin-wall injection molding performance.

[0078] Comparative Example 2, without the addition of conductive carbon black, resulted in a polypropylene composition with low electromagnetic shielding effectiveness and low tensile strength retention after heat aging treatment.

[0079] In Comparative Example 3, the mass ratio of conductive carbon black to multi-walled carbon nanotubes was too small, resulting in low electromagnetic shielding effectiveness and low tensile strength retention rate after thermal aging in the prepared polypropylene composition.

[0080] In Comparative Example 4, the mass ratio of conductive carbon black to multi-walled carbon nanotubes was too high, resulting in a polypropylene composition with low electromagnetic shielding effectiveness, low tensile strength retention after heat aging treatment, and unsatisfactory thin-wall injection molding performance.

[0081] The multi-walled carbon nanotubes in Comparative Example 5 had no carboxyl modification on their surface, resulting in a polypropylene composition with low tensile strength retention after heat aging treatment and unsatisfactory thin-wall injection molding performance.

[0082] In Comparative Example 6, replacing multi-walled carbon nanotubes with carbon fibers resulted in a polypropylene composition with low electromagnetic shielding effectiveness, low tensile strength retention after heat aging treatment, and unsatisfactory thin-wall injection molding performance.

[0083] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A polypropylene composition, characterized in that, It includes the following components by weight: 58-86 parts polypropylene, 5-17 parts conductive carbon black, 3-9 parts multi-walled carbon nanotubes, and 0.5-2 parts antioxidant. The surface of the multi-walled carbon nanotubes is modified with carboxyl groups; The mass ratio of the conductive carbon black to the multi-walled carbon nanotubes is (1.5~3):

1.

2. The polypropylene composition according to claim 1, characterized in that, The mass ratio of the conductive carbon black to the multi-walled carbon nanotubes is (1.5~2):

1.

3. The polypropylene composition according to claim 1, characterized in that, The oil absorption value of the conductive carbon black is 150~500ml / 100g.

4. The polypropylene composition according to claim 1, characterized in that, The carboxyl content in the multi-walled carbon nanotubes is ≥0.5 mmol / g.

5. The polypropylene composition according to claim 1, characterized in that, The combined mass of the conductive carbon black and multi-walled carbon nanotubes accounts for 8-30% of the total mass of the polypropylene composition.

6. The polypropylene composition according to claim 1, characterized in that, The antioxidant is at least one of the main antioxidant or the auxiliary antioxidant.

7. The polypropylene composition according to claim 1, characterized in that, The polypropylene composition further includes the following components in parts by weight: 0.1 to 2 parts of coupling agent and 0 to 5 parts of other additives.

8. A method for preparing the polypropylene composition according to any one of claims 1 to 7, characterized in that, Includes the following steps: Weigh each component according to the formula and mix them, then melt-blend and extrude granulate to obtain the polypropylene composition.

9. The use of the polypropylene composition according to any one of claims 1 to 7 in the preparation of electronic device housings or automotive parts.

10. A polypropylene component, characterized in that, It is prepared by any of the polypropylene compositions described in claims 1 to 7.

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