A conductive foamed polypropylene bead with high closed-cell ratio and its preparation method

Abstract

This invention relates to a high-closed-cell-rate conductive foamed polypropylene bead and its preparation method, belonging to the field of foamed polypropylene preparation technology. The invention first uses highly structured superconducting carbon black to prepare a conductive masterbatch with a small filler amount. Then, a co-extrusion process is used to place the superconducting carbon black in the shell layer as masterbatch, solving the problem of pore breakage caused by the addition of inorganic materials to the core layer structure. Simultaneously, combined with the cold air conveying system at the pressure relief port, the shell layer of the foamed beads can be rapidly cooled and crystallized, solving the risk of pore breakage caused by continuous cell growth. This improves the closed-cell rate of the conductive foamed polypropylene beads, thereby solving the problem of high pre-compression required by downstream customers before molding and reducing the equipment safety hazards caused by high pre-compression.

Description

Technical Field

[0001] This invention relates to a high closed-cell conductive foamed polypropylene bead and its preparation method, belonging to the field of foamed polypropylene preparation technology. Background Technology

[0002] Currently, conductive foamed polypropylene beads used in the market mainly rely on a large amount of inorganic conductive carbon black as filler to achieve 10. 6-9 The surface resistivity is excellent, such as Ω. However, polypropylene beads themselves have an independent closed-cell structure. With the filling of a large amount of inorganic conductive carbon black (over 50% content), the growth process of the bead cells exhibits characteristics such as... Figure 1 The anomalies shown include collapse, merging, and breakage, with a closure rate as low as 50 kg / m. 3 The closed-cell ratio was only 52%. This low closed-cell ratio limited the density of this foamed product to only 50 kg / m³. 3 If the density is forcibly reduced, the closed-cell rate will further decrease to 20 kg / m³. 3 The closed-cell ratio was only 31%, making normal molding virtually impossible and contradicting the product's lightweight design goals. This directly resulted in a high pre-compression process of 0.4-0.5 MPa being required during molding at the customer's site to create high internal pressure within the beads before steam molding could be used to mitigate shrinkage risks. However, prolonged high pre-compression poses potential safety hazards to customer equipment, and currently, there is no technology to solve this technical challenge.

[0003] To address the aforementioned problems, this invention provides a high-closed-cell-ratio conductive foamed polypropylene bead and its preparation method through research and improvement. Summary of the Invention

[0004] The purpose of this invention is to provide a high closed-cell rate conductive foamed polypropylene bead and its preparation method. By using superconducting carbon black with a high structure, the risk of pore breakage caused by excessive filling is reduced. At the same time, a co-extrusion "core-shell" process is adopted, placing the conductive carbon black only in the shell layer, which solves the problem of pore breakage caused by the addition of inorganic materials in the core layer structure. Combined with the cold air device at the pressure relief port in the process, the shell layer of the foamed bead can be rapidly cooled and crystallized, solving the risk of pore breakage caused by continuous cell growth. This can improve the closed-cell rate of conductive foamed polypropylene beads, thereby solving the problem of high pre-compression required by downstream customers before molding and eliminating the safety hazards caused by high pre-compression.

[0005] To achieve the above objectives, the present invention adopts the following technical solution.

[0006] The first aspect of this invention provides a method for preparing high-closed-cell conductive foamed polypropylene beads, comprising the following steps:

[0007] S1. Preparation of conductive masterbatch

[0008] Polypropylene powder, superconducting carbon black, and lubricant are mixed in proportion and then mixed and dispersed evenly in an internal mixer. At the same time, they are further mixed and granulated by a twin-screw extruder to obtain conductive masterbatch for the shell layer.

[0009] S2. Preparation of foamed polypropylene masterbatch

[0010] First, polypropylene resin A, the conductive masterbatch prepared in step S1, antioxidant, and lubricant are mixed in proportion to obtain a shell mixture; then, polypropylene resin B, nucleating agent, and lubricant are mixed in proportion to obtain a core mixture; then, the shell mixture and the core mixture are co-extruded to obtain foamed polypropylene masterbatch.

[0011] S3. Preparation of high closed-cell conductive foamed polypropylene beads

[0012] The foamed polypropylene masterbatch prepared in step 2 is put into a reactor and heated and pressurized with water as the dispersion medium. When the predetermined foaming temperature and pressure are reached, the pressure is instantly released to atmospheric pressure. At the same time, the foamed polypropylene beads are rapidly cooled and crystallized by cold air to obtain high closed-cell conductive foamed polypropylene beads.

[0013] Further, in step S1, the components, by weight, are: 79-89 parts of polypropylene powder, 8-16 parts of superconducting carbon black, and 3-5 parts of lubricant.

[0014] Furthermore, the specific surface area of ​​the superconducting carbon black is 650-800 m². 2 / g, oil absorption value is 365-380ml / 100g.

[0015] Furthermore, the lubricant is one or more of polyethylene wax, polypropylene wax, stearic acid, and stearamide.

[0016] Further, in step S2, the components of the shell mixture, by weight, are: 15-82 parts of polypropylene resin A, 15-80 parts of the conductive masterbatch prepared in S1, 2-3 parts of antioxidant, and 1-2 parts of lubricant; the components of the core mixture, by weight, are: 95-100 parts of polypropylene resin B, 2-3 parts of nucleating agent, and 1-2 parts of lubricant.

[0017] Furthermore, the polypropylene resin A is a low-crystallinity random copolymer polypropylene resin with a melting point of 128-133℃; and the polypropylene resin B is a high-crystallinity random copolymer polypropylene resin with a melting point of 145-150℃.

[0018] Furthermore, the antioxidant is one or more of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, tris[2,4-di-tert-butylphenyl]phosphite, and tris(butylcresol)butane.

[0019] Furthermore, the nucleating agent is an inorganic nucleating agent with a serrated, flaky structure and a size of 3-5 μm, including one or more of talc, montmorillonite, calcium carbonate, silicon dioxide, zinc borate, and titanium dioxide.

[0020] Furthermore, in step S3, the heating and pressurizing reaction conditions are: 149-150℃, 2.0-2.2 MPa; the predetermined foaming temperature and pressure are: 149-150℃, 2.0-2.2 MPa; and the temperature of the cold air is 0-20℃, preferably 3-10℃.

[0021] A second aspect of the present invention provides conductive foamed polypropylene beads with high closed-cell ratio prepared by the above-described preparation method.

[0022] The beneficial effects and advantages of this invention compared to the prior art are as follows:

[0023] 1. Conductive foamed polypropylene beads, 50kg / m², after process improvement 3 The closed-cell ratio can be increased to over 85%;

[0024] 2. The closed-cell ratio of the high-ratio conductive foam material was optimized and improved to 20 kg / m³. 3 The closed-cell rate reached 69%, further reducing the customer's usage cost and promoting the expansion of the application field of conductive foamed polypropylene beads.

[0025] 3. It solved the problem of downstream customers having to apply high pre-pressure before molding, and eliminated the risks associated with high pressure equipment. Attached Figure Description

[0026] Figure 1 The image is a scanning electron microscope image of foamed polypropylene beads obtained by filling a large amount of conductive carbon black in the prior art.

[0027] Figure 2 The image shows a scanning electron microscope (SEM) image of the conductive foamed polypropylene beads prepared according to an embodiment of the present invention. Detailed Implementation

[0028] The present invention will be further illustrated below with reference to specific embodiments. The present invention is implemented based on the inventive technical solution, and detailed implementation methods and operating steps are provided. However, the scope of protection of the present invention is not limited to the following embodiments. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions.

[0029] A method for preparing high closed-cell conductive foamed polypropylene beads includes the following steps:

[0030] S1. Preparation of conductive masterbatch

[0031] 79-89 parts of polypropylene powder, 8-16 parts of superconducting carbon black, and 3-5 parts of lubricant are mixed and then passed through an internal mixer and a twin-screw extruder in sequence to obtain a conductive masterbatch for the shell layer.

[0032] The specific surface area of ​​the superconducting carbon black is 650-800 m². 2 / g, oil absorption value is 365-380ml / 100g.

[0033] S2. Preparation of foamed polypropylene masterbatch

[0034] First, 15-82 parts of low-crystallinity random copolymer polypropylene resin A with a melting point of 128-133℃, 15-80 parts of conductive masterbatch prepared by S1, 2-3 parts of antioxidant, and 1-2 parts of lubricant are mixed to obtain a shell mixture; then, 95-100 parts of high-crystallinity random copolymer polypropylene resin B with a melting point of 145-150℃, 2-3 parts of nucleating agent, and 1-2 parts of lubricant are mixed to obtain a core mixture; then, the shell mixture and the core mixture are subjected to a co-extrusion process to obtain foamed polypropylene masterbatch.

[0035] The antioxidant is one or more of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, tris[2,4-di-tert-butylphenyl]phosphite, and tris(butylcresol)butane.

[0036] The nucleating agent is an inorganic nucleating agent with a serrated, flaky structure and a size of 3-5 μm, including one or more of talc, montmorillonite, calcium carbonate, silicon dioxide, zinc borate, and titanium dioxide.

[0037] S3. Preparation of high closed-cell conductive foamed polypropylene beads

[0038] The foamed polypropylene masterbatch prepared in step 2 is put into a reactor and heated and pressurized with water as the dispersion medium. When the predetermined foaming temperature and pressure are reached, the foamed polypropylene masterbatch generates outward expansion pressure, which is instantly released to atmospheric pressure through the pressure relief port. At the same time, the pressure relief port is used to transport cold air to rapidly cool and crystallize the foamed polypropylene beads, thus obtaining high closed-cell conductive foamed polypropylene beads.

[0039] The temperature of the cold air is 0-20℃, preferably 3-10℃.

[0040] Examples 1-10

[0041] In the preparation methods of Examples 1-10 of this invention,

[0042] The components of step S1, by weight, are as follows:

[0043] Polypropylene powder, 82 parts;

[0044] Superconducting carbon black, 15 parts;

[0045] Lubricant, 3 parts.

[0046] The components in step S2, by weight, are as follows:

[0047] Polypropylene resin A was added in amounts of 77 parts, 77 parts, 64 parts, 64 parts, 64 parts, 44 parts, 44 parts, 44 parts, 30.3 parts, and 30.3 parts in Examples 1-10, respectively.

[0048] The conductive masterbatch prepared by S1 was added in Examples 1-10 in amounts of 20 parts, 20 parts, 33 parts, 33 parts, 33 parts, 53 parts, 53 parts, 53 parts, 66.7 parts, and 66.7 parts, respectively. It should be noted that the content of superconducting carbon black in Table 1 was calculated based on the content of superconducting carbon black in the conductive masterbatch prepared by S1 in the entire formula.

[0049] Antioxidant, 2 parts;

[0050] Lubricant, 1 part;

[0051] Polypropylene resin B, 97 parts;

[0052] Nucleating agent, 2 parts;

[0053] Lubricant, 1 part.

[0054] In step S3, the foaming temperature and the cold air temperature are both as shown in Table 1 below.

[0055] Table 1

[0056]

[0057] Product characterization and performance testing

[0058] (1) Scanning electron microscopy test

[0059] This invention uses the conductive foamed polypropylene beads prepared in the examples provided in this paper for scanning electron microscopy (SEM) testing. The SEM used in this invention was manufactured by a Japanese company, model JSM-7900F. The test results are as follows: Figure 2 As shown.

[0060] (2) Closed-pore ratio test

[0061] The present invention takes the conductive foamed polypropylene beads prepared in Examples 1-10 as examples to test the closed-cell rate. The test method refers to the national standard GB-T 10799-2008 "Determination of open and closed cell volume percentage of rigid foam plastics". The test results are shown in Table 1.

[0062] (3) Surface resistance measurement

[0063] The present invention takes the conductive foamed polypropylene beads prepared in Examples 1-10 as examples to conduct surface resistance tests. The test method refers to the national standard GB / T 31838.3-2019 Dielectric and resistive properties of solid insulating materials Part 3: Resistive properties (DC method) Surface resistance and surface resistivity. The test results are shown in Table 1.

[0064] (4) Determination of molding appearance

[0065] The present invention takes the conductive foamed polypropylene beads prepared in Examples 1-10 as examples to determine the molding appearance, and the determination results are shown in Table 1.

[0066] In summary, as shown in Table 1, a surface resistivity of 10 Ω·cm has been achieved when the superconducting carbon black content is between 5% and 8%. 6-9 Ω and good surface, while the temperature of cold air has a great influence on the closed-cell rate of beads, and 3-10℃ is the best.

[0067] The above description only illustrates the technical solution of the present invention with reference to preferred embodiments. However, those skilled in the art should be able to make changes in specific implementation methods and application scope based on the ideas of the embodiments of the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of the present invention should be included within the scope of the claims of the present invention.

Claims

1. A method for preparing high closed-cell conductive foamed polypropylene beads, characterized in that, Includes the following steps: S1. Preparation of conductive masterbatch Polypropylene powder, superconducting carbon black, and lubricant are mixed in a certain proportion and then passed through a mixer and a twin-screw extruder in sequence to obtain a conductive masterbatch for the shell layer. S2. Preparation of foamed polypropylene masterbatch First, polypropylene resin A, the conductive masterbatch prepared in step S1, antioxidant, and lubricant are mixed in proportion to obtain a shell mixture; then, polypropylene resin B, nucleating agent, and lubricant are mixed in proportion to obtain a core mixture; then, the shell mixture and the core mixture are co-extruded to obtain foamed polypropylene masterbatch with a "core-shell" structure. S3. Preparation of high closed-cell conductive foamed polypropylene beads The foamed polypropylene masterbatch prepared in step 2 is put into a reaction vessel, and water is used as the dispersion medium. The mixture is heated and pressurized until the predetermined foaming temperature and pressure are reached. Then, the pressure is instantly released to atmospheric pressure through the pressure relief port. At the same time, the shell of the foamed polypropylene beads is rapidly cooled and crystallized by the cold air at the pressure relief port to obtain high closed-cell conductive foamed polypropylene beads. In step S1, the components, by weight, are: 79-89 parts of polypropylene powder, 8-16 parts of superconducting carbon black, and 3-5 parts of lubricant. The specific surface area of ​​the superconducting carbon black is 650-800 m². 2 / g, oil absorption value is 365-380ml / 100g; In step S2, the components of the shell mixture, by weight, are: 64 or 44 parts of polypropylene resin A, 15-80 parts of the conductive masterbatch prepared in S1, 2-3 parts of antioxidant, and 1-2 parts of lubricant; the mass fraction of superconducting carbon black in the shell mixture is 5%-8%; the components of the core mixture, by weight, are: 95-100 parts of polypropylene resin B, 2-3 parts of nucleating agent, and 1-2 parts of lubricant. In step S3, the heating and pressurizing reaction conditions are: 149-150℃, 2.0-2.2 MPa; the predetermined foaming temperature and pressure are: 149-150℃, 2.0-2.2 MPa; and the temperature of the cold air is 3-10℃.

2. The method for preparing high closed-cell conductive foamed polypropylene beads according to claim 1, characterized in that, The polypropylene resin A is a low-crystallinity random copolymer polypropylene resin with a melting point of 128-133℃; the polypropylene resin B is a high-crystallinity random copolymer polypropylene resin with a melting point of 145-150℃.

3. The method for preparing high closed-cell conductive foamed polypropylene beads according to claim 1, characterized in that, The antioxidant is one or more of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, tris[2,4-di-tert-butylphenyl]phosphite, and tris(butylcresol)butane.

4. The method for preparing high closed-cell conductive foamed polypropylene beads according to claim 1, characterized in that, The nucleating agent is an inorganic nucleating agent with a serrated, flaky structure and a size of 3-5 μm, including one or more of talc, montmorillonite, calcium carbonate, silicon dioxide, zinc borate, and titanium dioxide.

5. High closed-cell conductive foamed polypropylene beads prepared by the method for preparing high closed-cell conductive foamed polypropylene beads according to any one of claims 1-4.

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