A thermally conductive polypropylene sheet and a method for preparing the same

Abstract

The application relates to the technical field of materials, in particular to a heat-conducting polypropylene sheet and a preparation method thereof. The heat-conducting polypropylene sheet is prepared from the following raw materials in parts by weight: 95-105 parts of polypropylene matrix resin, 6-12 parts of graphene microsheet, 2-6 parts of silane coupling agent, 7-16 parts of heat-conducting filler, 4-8 parts of compatilizer, 10-14 parts of dispersing agent and 0.4-1.0 parts of antioxidant. The application adopts the graphene microsheet and the heat-conducting filler such as boron nitride to synergistically reinforce the polypropylene, a three-dimensional heat-conducting network is constructed in the PP matrix through the GNPs and the BNFs, the heat-conducting coefficient of the composite material is greater than or equal to 1.0 W / (m*K), is about 7 times more than that of pure PP, and the problems that heat of the floor heating pipe is slowly spread horizontally and locally accumulated heat are effectively solved.

Description

Technical Field

[0001] This invention relates to the field of materials technology, and in particular to a thermally conductive polypropylene sheet and its preparation method. Background Technology

[0002] In traditional water-based underfloor heating systems, the heating pipes are embedded in the leveling layer or insulation modules. Heat is transferred from the hot water inside the pipes to the pipe walls and then radiates to the floor. However, traditional underfloor heating pipes are generally made of high-molecular materials such as heat-resistant polyethylene, cross-linked polyethylene, and random copolymer polypropylene. These materials have low thermal conductivity, typically in the range of 0.35~0.45 W / (m·K). This results in heat not spreading quickly laterally within the pipe walls, leading to localized heat accumulation around the pipe walls. Furthermore, heat conduction downwards is impaired, and some heat is lost directly through the insulation layer, causing energy waste and slow heating response.

[0003] To address the aforementioned issues, existing technologies typically employ an aluminum foil heat-dissipating pad on the surface of the insulation board. This utilizes the high thermal conductivity of the aluminum foil to spread heat from the pipe wall laterally and conduct it evenly downwards. However, aluminum foil heat-dissipating pads have significant drawbacks in practical applications: firstly, the aluminum foil reflects heat back to the ground, preventing effective heat radiation from reaching the room, thus affecting heating efficiency and wasting energy; secondly, thin aluminum foil is corroded by the cement backfill layer during wet installation of water-based underfloor heating systems, leading to deterioration of thermal conductivity and loosening of the floor layer; and thirdly, air gaps easily exist between the aluminum foil and the water pipes, increasing interfacial thermal resistance. Therefore, there is an urgent need to develop a floor heating heat-conducting material with excellent thermal conductivity, corrosion resistance, and the ability to be extruded into ultra-thin sheets to replace traditional aluminum foil heat-dissipating pads.

[0004] Based on the above, this invention proposes a thermally conductive polypropylene sheet and its preparation method, which can effectively solve the above problems. Summary of the Invention

[0005] The purpose of this invention is to provide a thermally conductive polypropylene sheet and its preparation method.

[0006] To achieve the above objectives, the present invention provides a thermally conductive polypropylene sheet, which is composed of the following raw materials in parts by weight:

[0007] 95-105 parts of polypropylene matrix resin, 6-12 parts of graphene micro flakes, 2-6 parts of silane coupling agent, 7-16 parts of thermally conductive filler, 4-8 parts of compatibilizer, 10-14 parts of dispersant, and 0.4-1.0 parts of antioxidant.

[0008] Preferably, the polypropylene matrix resin is copolymer polypropylene (PP-R) or homopolymer polypropylene (PP-H), and the melt flow rate (230℃ / 2.16 kg) is 2~8 g / 10 min.

[0009] Preferably, the graphene microplates (GNP) have a diameter of 5~20 μm, ≤10 layers, and a purity of ≥98%.

[0010] Preferably, the silane coupling agent is a fluorinated silane coupling agent. In one embodiment, the fluorinated silane coupling agent is dodecafluoroheptylpropyltrimethoxysilane.

[0011] Preferably, the thermally conductive filler is selected from one or a combination of two or more of boron nitride (BN), aluminum nitride (AlN), and aluminum oxide (Al2O3).

[0012] Preferably, the dispersant is a fluorinated ethylene propylene copolymer.

[0013] Preferably, the antioxidant is at least one of a polyhedral hindered phenolic antioxidant or a phosphite antioxidant.

[0014] Preferably, the multi-functional hindered phenolic antioxidant includes one of the following: pentaerythritol tetrakis[methyl-β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, or N,N'-bis-(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl)hexamethylenediamine.

[0015] Preferably, the phosphite antioxidant includes one of tris[2,4-di-tert-butylphenyl]phosphite or pentaerythritol distearate diphosphite.

[0016] Preferably, the compatibilizer is maleic anhydride-grafted polypropylene (PP-g-MAH), in one embodiment of which the type is 332K, the grafting rate is 1~1.2%, the density is 0.90 g / cm3, and the melt flow index is 200.0 g / 10 min.

[0017] This invention application also provides a method for preparing a thermally conductive polypropylene sheet, the method comprising the following steps:

[0018] (1) Dissolve the silane coupling agent in an aqueous ethanol solution with a volume concentration of 50-55% to make the concentration of the silane coupling agent in the mixture 10-11wt%. Then add hexagonal boron nitride and soak for 30-35 minutes. After taking it out, place it in an oven at 80±5℃ to dry it to obtain silane coupling agent modified hexagonal boron nitride.

[0019] (2) The dried polypropylene resin, sericite, maleic anhydride-grafted polypropylene, fluorinated ethylene propylene copolymer, and antioxidant are put into a high-speed mixer and mixed at 500-1000 rpm for 5-10 minutes; then graphene microplates, silane coupling agent modified hexagonal boron nitride, and aluminum oxide are added, and the mixture is continued for 8-15 minutes to obtain a uniformly mixed premix.

[0020] (3) The premixed material is fed into a twin-screw extruder for melt blending, extrusion and granulation. The extrusion process parameters are: screw speed 150~300 rpm, feed speed 10~30 rpm; the temperature of each zone of the extruder is set as follows: zone 1 180~190℃, zone 2 190~200℃, zone 3 200~215℃, zone 4 215~225℃, zone 5 220~230℃, and die head temperature 220~235℃.

[0021] (4) The granules obtained in step (3) are melted and plasticized by a single screw extruder, and extruded into sheets by a T-die. The sheets are then calendered, cooled and shaped, drawn and wound up by three rollers. The extrusion sheet process parameters are: extruder temperature 200~235℃, T-die temperature 220~240℃, three roller temperature 40~70℃, and drawing speed 5~20 m / min.

[0022] (5) Cut and roll the sheet according to the width, and control the sheet thickness tolerance to ±0.01 mm.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. This invention uses graphene microsheets and thermally conductive fillers such as boron nitride to synergistically reinforce polypropylene. A three-dimensional thermally conductive network is constructed in the PP matrix through GNP and BNF, so that the thermal conductivity of the composite material is ≥1.0 W / (m·K), which is more than 7 times that of pure PP, effectively solving the problems of slow horizontal heat spread and local heat accumulation in underfloor heating pipes.

[0025] 2. By adopting a graphene and boron nitride / alumina composite system, the sheet of this invention maintains excellent electrical insulation properties with a volume resistivity ≥1.0×10¹²Ω·cm, avoiding electrochemical corrosion and safety hazards that may occur in the humid environment of the underfloor heating system, and without damaging the cement backfill layer and the floor decoration material.

[0026] 3. This invention achieves continuous and stable production of 0.16 mm ultra-thin thermally conductive PP sheets through formula optimization and T-die casting extrusion process. The sheets exhibit good uniformity and high flexibility, allowing for direct application to the surface of underfloor heating modules for convenient installation. Compared to aluminum foil heat-dissipating pads, the PP thermally conductive sheets of this invention have a shorter thermal response time and better surface temperature uniformity under the same heat source conditions. This effectively solves the heat loss problem caused by the reflected heat radiation from aluminum foil, enabling rapid lateral heat distribution and uniform downward conduction of heat from the pipe wall, avoiding localized heat accumulation, and reducing the energy consumption of the underfloor heating system. The thermally conductive PP sheets are inherently water-resistant, acid and alkali-resistant, and resistant to cement corrosion, ensuring stable performance in long-term use in wet underfloor heating installation environments, overcoming the defect of aluminum foil heat-dissipating pads being easily corroded and failing by cement.

[0027] 4. The raw materials for this invention are abundant and reasonably priced in China, which means that there are no high cost restrictions on its large-scale production; at the same time, the preparation method is simple and the overall production cost is not high, which is conducive to large-scale industrial production. Detailed Implementation

[0028] Example 1

[0029] (1) Dissolve the silane coupling agent in an aqueous ethanol solution with a volume concentration of 50% to make the concentration of the silane coupling agent in the mixture 10wt%. Then add hexagonal boron nitride and soak for 30min. After taking it out, place it in an oven at 80±5℃ to dry it to obtain silane coupling agent modified hexagonal boron nitride.

[0030] (2) The dried polypropylene resin, sericite, maleic anhydride grafted polypropylene, fluorinated ethylene propylene copolymer and antioxidant were put into a high-speed mixer and mixed at 500 rpm for 10 minutes; then graphene micro flakes, silane coupling agent modified hexagonal boron nitride and aluminum oxide were added and mixed for another 15 minutes to obtain a uniformly mixed premix.

[0031] (3) The premixed material is fed into a twin-screw extruder for melt blending, extrusion and granulation. The extrusion process parameters are: screw speed 150 rpm, feed speed 10 rpm; the temperature of each zone of the extruder is set as follows: zone 1 180~190℃, zone 2 190~200℃, zone 3 200~215℃, zone 4 215~225℃, zone 5 220~230℃, and die head temperature 220~235℃.

[0032] (4) The granules obtained in step (3) are melted and plasticized by a single screw extruder, and extruded into sheets by a T-die. The sheets are then calendered, cooled and shaped, drawn and wound up by three rollers. The extrusion sheet process parameters are: extruder temperature 200~235℃, T-die temperature 220~240℃, three roller temperature 40~70℃, and drawing speed 5~20 m / min.

[0033] (5) Cut and roll the sheet according to the width, and control the sheet thickness tolerance to ±0.01 mm.

[0034] Example 2

[0035] (1) Dissolve the silane coupling agent in an aqueous ethanol solution with a volume concentration of 55% to make the concentration of the silane coupling agent in the mixture 11wt%. Then add hexagonal boron nitride and soak for 35min. After taking it out, place it in an oven at 80±5℃ to dry it to obtain silane coupling agent modified hexagonal boron nitride.

[0036] (2) The dried polypropylene resin, sericite, maleic anhydride grafted polypropylene, fluorinated ethylene propylene copolymer and antioxidant were put into a high-speed mixer and mixed at 1000 rpm for 5 minutes; then graphene micro flakes, silane coupling agent modified hexagonal boron nitride and aluminum oxide were added and mixed for another 8 minutes to obtain a uniformly mixed premix.

[0037] (3) The premixed material is fed into a twin-screw extruder for melt blending, extrusion and granulation. The extrusion process parameters are: screw speed 300 rpm, feed speed 30 rpm; the temperature of each zone of the extruder is set as follows: zone 1 180~190℃, zone 2 190~200℃, zone 3 200~215℃, zone 4 215~225℃, zone 5 220~230℃, and die head temperature 220~235℃.

[0038] (4) The granules obtained in step (3) are melted and plasticized by a single screw extruder, and extruded into sheets by a T-die. The sheets are then calendered, cooled and shaped, drawn and wound up by three rollers. The extrusion sheet process parameters are: extruder temperature 200~235℃, T-die temperature 220~240℃, three roller temperature 40~70℃, and drawing speed 5~20 m / min.

[0039] (5) Cut and roll the sheet according to the width, and control the sheet thickness tolerance to ±0.01 mm.

[0040] Example 3

[0041] (1) Dissolve the silane coupling agent in an aqueous ethanol solution with a volume concentration of 55% to make the concentration of the silane coupling agent in the mixture 11wt%. Then add hexagonal boron nitride and soak for 35min. After taking it out, place it in an oven at 80±5℃ to dry it to obtain silane coupling agent modified hexagonal boron nitride.

[0042] (2) The dried polypropylene resin, sericite, maleic anhydride-grafted polypropylene, fluorinated ethylene propylene copolymer, and antioxidant were put into a high-speed mixer and mixed at 1000 rpm for 10 minutes. Then graphene microplates, silane coupling agent modified hexagonal boron nitride, and aluminum oxide were added and mixed for another 15 minutes to obtain a uniformly mixed premix.

[0043] (3) The premixed material is fed into a twin-screw extruder for melt blending, extrusion and granulation. The extrusion process parameters are: screw speed 300 rpm, feed speed 30 rpm; the temperature of each zone of the extruder is set as follows: zone 1 180~190℃, zone 2 190~200℃, zone 3 200~215℃, zone 4 215~225℃, zone 5 220~230℃, and die head temperature 220~235℃.

[0044] (4) The granules obtained in step (3) are melted and plasticized by a single screw extruder, and extruded into sheets by a T-die. The sheets are then calendered, cooled and shaped, drawn and wound up by three rollers. The extrusion sheet process parameters are: extruder temperature 200~235℃, T-die temperature 220~240℃, three roller temperature 40~70℃, and drawing speed 5~20 m / min.

[0045] (5) Cut and roll the sheet according to the width, and control the sheet thickness tolerance to ±0.01 mm.

[0046] Comparative Example 1

[0047] Weigh the specific raw materials according to Table 1. Unlike Example 3, no silane coupling agent was added.

[0048] Comparative Example 2

[0049] Weigh the specific raw materials according to Table 1. The difference from Example 3 is that the silane coupling agent is a fluorine-free silane coupling agent KH560.

[0050] Comparative Example 3

[0051] Weigh the specific raw materials according to Table 1. The difference from Example 3 is that the silane coupling agent is a fluorine-free silane coupling agent KH550.

[0052] Comparative Example 4

[0053] Weigh the specific raw materials according to Table 1. Unlike Example 3, aluminum oxide was not added.

[0054] Table 1

[0055]

[0056] Performance testing

[0057] Tensile yield strength was determined according to ISO 527-2 standard; thermal conductivity was determined according to GB / T 10295 standard; volume resistivity was determined according to GB / T 1410. The test results are shown in Table 2.

[0058] Table 2

[0059]

[0060] The foregoing description of specific exemplary embodiments of the invention is for illustrative and explanatory purposes. These descriptions are not intended to limit the invention to the precise forms disclosed, and it will be apparent that many changes and variations can be made in accordance with the foregoing teachings. The exemplary embodiments were chosen and described in order to explain the specific principles of the invention and its practical application, thereby enabling those skilled in the art to implement and utilize various different exemplary embodiments of the invention, as well as various different choices and variations. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A thermally conductive polypropylene sheet, characterized in that, The thermally conductive polypropylene sheet is composed of the following parts by weight of raw materials: The composition includes 95-105 parts of polypropylene matrix resin, 6-12 parts of graphene microplates, 2-6 parts of silane coupling agent, 7-16 parts of thermally conductive filler, 4-8 parts of compatibilizer, 10-14 parts of dispersant, and 0.4-1.0 parts of antioxidant.

2. The thermally conductive polypropylene sheet according to claim 1, characterized in that, The polypropylene matrix resin is copolymer polypropylene or homopolymer polypropylene.

3. The thermally conductive polypropylene sheet according to claim 1, characterized in that, The graphene microsheets have a diameter of 5~20μm, ≤10 layers, and a purity of ≥98%.

4. The thermally conductive polypropylene sheet according to claim 1, characterized in that, The silane coupling agent is a fluorinated silane coupling agent.

5. The thermally conductive polypropylene sheet according to claim 1, characterized in that, The thermally conductive filler is selected from one or more of boron nitride, aluminum nitride, and aluminum oxide.

6. The thermally conductive polypropylene sheet according to claim 1, characterized in that, The dispersant is a fluorinated ethylene propylene copolymer.

7. The thermally conductive polypropylene sheet according to claim 1, characterized in that, The antioxidant is at least one of the following: a polyprotic hindered phenolic antioxidant or a phosphite antioxidant.

8. The thermally conductive polypropylene sheet according to claim 7, characterized in that, The multi-component hindered phenolic antioxidant is pentaerythritol tetrakis[methyl-β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]; the phosphite antioxidant is tris[2,4-di-tert-butylphenyl]phosphite.

9. The thermally conductive polypropylene sheet according to claim 1, characterized in that, The compatibilizer is maleic anhydride-grafted polypropylene.

10. A method for preparing the thermally conductive polypropylene sheet according to claim 1, characterized in that, The preparation method includes the following steps: (1) Dissolve the silane coupling agent in an aqueous ethanol solution with a volume concentration of 50-55% to make the concentration of the silane coupling agent in the mixture 10-11wt%. Then add hexagonal boron nitride and soak for 30-35 minutes. After taking it out, place it in an oven at 80±5℃ to dry it to obtain silane coupling agent modified hexagonal boron nitride. (2) The dried polypropylene resin, sericite, maleic anhydride-grafted polypropylene, fluorinated ethylene propylene copolymer, and antioxidant are put into a high-speed mixer and mixed at 500-1000 rpm for 5-10 minutes; then graphene microplates, silane coupling agent modified hexagonal boron nitride, and aluminum oxide are added, and the mixture is continued for 8-15 minutes to obtain a uniformly mixed premix. (3) The premixed material is fed into a twin-screw extruder for melt blending, extrusion and granulation. The extrusion process parameters are: screw speed 150~300 rpm, feed speed 10~30 rpm; the temperature of each zone of the extruder is set as follows: zone 1 180~190℃, zone 2 190~200℃, zone 3 200~215℃, zone 4 215~225℃, zone 5 220~230℃, and die head temperature 220~235℃. (4) The granules obtained in step (3) are melted and plasticized by a single screw extruder, and extruded into sheets by a T-die. The sheets are then calendered, cooled and shaped, drawn and wound up by three rollers. The extrusion sheet process parameters are: extruder temperature 200~235℃, T-die temperature 220~240℃, three roller temperature 40~70℃, and drawing speed 5~20 m / min. (5) Cut and roll the sheet according to the width, and control the sheet thickness tolerance to ±0.01 mm.

Images