An anisotropic insulating and heat-conducting sheet and a preparation method thereof

Abstract

The present invention discloses an anisotropic insulating and heat-conducting sheet, which comprises a heat-conducting sheet. The raw materials for preparing the anisotropic insulating and heat-conducting sheet at least include a flexible polymer material, carbon fibers, spherical micropowders and a flame retardant, and the carbon fibers are oriented in the thickness direction of the heat-conducting sheet. The present invention also discloses a method for preparing the anisotropic insulating and heat-conducting sheet. The anisotropic insulating and heat-conducting sheet of the invention at least includes a flexible polymer material, carbon fibers, spherical micropowders and a flame retardant, so that irregular heat-conducting fillers are mixed in the thermosetting flexible polymer material, and the fibrous heat-conducting fillers are oriented in the flow direction by the action of shear force, and it is a heat-conducting sheet with excellent heat-conducting performance and insulating performance.

Description

Technical Field

[0001] The present invention relates to the technical field of thermal conductive interface materials and preparation, and particularly relates to an insulating and thermally conductive material and a preparation method thereof. Background Art

[0002] With the rapid development of data networks, electronic and electrical products are developing towards intelligence, high speed and complexity. The densification of integrated circuits will approach the physical limit, which will lead to more and more heat generated during the operation of product equipment. The heat cannot be quickly transferred and dissipated, affecting the use stability and service life of electronic products. Therefore, the heat problem has become the primary problem to be solved in the development of electronic products.

[0003] For efficient heat dissipation, a thermal conductive interface material is filled between the semiconductor chip and the radiator and the cooling fan. Conventional thermal conductive materials on the market require a high filling amount of ceramic powder to obtain good thermal conductivity, which loses the softness and conformability of the material, and the high filling amount will lead to a decline in the material stability and life. Utilizing the anisotropic characteristics of thermal conductive fillers, good thermal conductivity can also be obtained with a small filling amount. Thermal conductive fillers with anisotropic characteristics include graphite, boron nitride, alumina whiskers, zinc oxide whiskers, carbon fiber, etc. The thermal conductivity of carbon fiber in the fiber direction can reach 1500 w / m·K. If a small amount of carbon fiber is filled and the carbon fiber is oriented along the thickness direction of the product, not only will the product retain good flexibility, but also excellent thermal conductivity will be obtained.

[0004] At present, there are some thermal conductive sheets on the market that utilize the orientation of carbon fiber to obtain an ultra-high thermal conductivity. However, due to the good electrical conductivity of carbon fiber itself, the product is not insulated, and there is a risk of voltage breakdown of the related circuit board during the application process. Summary of the Invention

[0005] To solve the above problems, the purpose of the present invention is to obtain an anisotropic thermal conductive sheet with good flexibility, high thermal conductivity and insulation by mixing and orienting carbon fiber and a high-flexibility polymer material.

[0006] To achieve the above purpose, the present invention adopts the following scheme:

[0007] An anisotropic insulating and thermally conductive sheet, including a thermally conductive sheet. The raw materials for preparing the anisotropic insulating and thermally conductive sheet at least include a flexible polymer material, carbon fiber, spherical micropowder and a flame retardant, and the carbon fiber is oriented in the thickness direction of the thermally conductive sheet.

[0008] As a further scheme, the raw materials of the present invention at least include 150 - 300 parts by weight of flexible polymer material, 500 - 800 parts by weight of carbon fiber, 1200 - 1800 parts by weight of spherical micropowder and 150 - 200 parts by weight of flame retardant.

[0009] As a further solution, the flexible polymer material described in the present invention is one or a mixture of two or more of liquid acrylic resin, epoxy resin, polyurethane resin, unsaturated polyester resin, and silicone resin.

[0010] As a further solution, the raw materials of the present invention further include 100-150 parts by weight of vinyl silicone oil, and the viscosity of the vinyl silicone oil is 500-100,000 mPa·s.

[0011] As a further solution, the raw materials of the present invention further include 80-120 parts by weight of dimethyl silicone oil, 0.05-0.2 parts by weight of delay inhibitor, 3-6 parts by weight of H-containing silicone oil, and 1-3 parts by weight of platinum water catalyst.

[0012] As a further solution, the spherical micro-powder described in the present invention is a compound powder containing alumina and silicate powder, and the average particle size of the spherical micro-powder is 0.1-5 μm. Preferably, the spherical micro-powder further contains one or a mixture of two or more of boron nitride, aluminum nitride, and silicon carbide in a small amount.

[0013] As a further solution, the carbon fiber described in the present invention is one of polyacrylonitrile-based carbon fiber, pitch-based carbon fiber, viscose-based carbon fiber, phenolic-based carbon fiber, and vapor-grown carbon fiber with a surface insulation coating, and the average diameter of the carbon fiber is 2-30 μm and the length is 50-300 μm.

[0014] As a further solution, a polymer coating is formed on the surface of the heat-conducting sheet of the present invention by coating a polymer coating. The polymer coating includes 80-120 parts by weight of vinyl silicone oil, 40-65 parts by weight of dimethyl silicone oil, 0.05-0.2 parts by weight of delay inhibitor, 2-5 parts by weight of H-containing silicone oil, 1-3 parts by weight of platinum water catalyst, and 150-200 parts by weight of long-chain alkyl siloxane according to weight. Preferably, the thickness of the polymer coating described in the present invention is ≤50 μm. In the present invention, the polymer coating on the heat-conducting sheet has adhesiveness, which is convenient for the assembly between the heat-conducting gasket and other components.

[0015] The present invention also provides a preparation method of an anisotropic insulating and heat-conducting sheet. By using the shear force, the fibrous heat-conducting filler is oriented in the flow direction to obtain an anisotropic insulating and heat-conducting sheet with excellent performance.

[0016] A preparation method of an anisotropic insulating and heat-conducting sheet includes

[0017] The step of preparing a heat-conducting pre-material: uniformly mixing carbon fiber, spherical micro-powder and a flame retardant in a flexible polymer material to prepare a heat-conducting pre-material;

[0018] Flow velocity shear orientation step: The above-mentioned thermal conductivity preform is extruded through an extruder to orient the carbon fibers in the flow velocity direction, and is heated and cured in a moldable movable mold groove to form a molded body;

[0019] Ultrasonic cutting step: The above-mentioned molded body is cut by ultrasonic cutting along the direction perpendicular to the flow velocity to obtain a thermally conductive sheet with carbon fibers oriented in the thickness direction.

[0020] In a further aspect, the preparation method of the present invention further includes a surface treatment step of the thermally conductive sheet. The surface treatment of the thermally conductive sheet is to form a polymer coating by coating a polymer coating on the surface of the thermally conductive sheet or to polish the surface of the thermally conductive sheet to make it smooth by polishing.

[0021] As a further aspect, in the preparation method of the present invention, after the step of preparing the thermal conductivity preform and before the flow velocity shear orientation step, it further includes the step of placing the uniformly mixed thermal conductivity preform in a vacuum chamber for vacuum pumping. The vacuum degree of the vacuum chamber is ≤ -0.09 Mpa, and the vacuum pumping time is ≥ 8 min.

[0022] As a further aspect, release films are attached around the mold device of the present invention. Preferably, the release film can be selected from but not limited to one of PET film, PI film, oiled paper, dripping film, thinners paper, anti-adhesive film, and anti-slip film.

[0023] As a further aspect, the extruder of the present invention is a screw extruder, and the extrusion nozzle of the extruder is a honeycomb extrusion nozzle; the cross-sectional area of a single pore in the honeycomb extrusion nozzle is ≤ 81 mm 2 , the wall thickness is ≤ 0.1 mm, and the length of the honeycomb extrusion nozzle is ≥ 5 cm. Further, the cross-sectional size of the honeycomb flow channel of the honeycomb extrusion nozzle is at least 30 mm × 30 mm, and the shape of a single pore is not limited and can be circular, oval, rectangular, square, other polygons, etc. Among them, equilateral symmetric polygons, circles, or ovals are more preferred.

[0024] As a further aspect, the extrusion flow channel of the extruder of the present invention is a conical flow channel. At least one flow splitting device is installed at the connection between the conical flow channel and the honeycomb extrusion nozzle. The end of the honeycomb extrusion nozzle is connected to the moldable movable mold groove, and a limiter for controlling the backward movement distance of the mold groove is installed at the end of the movable mold groove. Specifically, one end of the movable mold groove is sleeved with the end of the honeycomb extrusion nozzle. In this solution, by using a honeycomb extrusion nozzle, the possibility of carbon fiber orientation in the flow channel can be increased. One end of the movable mold groove is connected to the end of the honeycomb extrusion nozzle, so that the extrusion speed of the preform is consistent with the backward movement speed, reducing the interference of air in the mold cavity, and heating and curing the mold in the movable mold groove to form a mold.

[0025] As a further solution, in the flow velocity shear orientation step of the present invention, hot air curing is adopted in a blast oven, the temperature of the oven is set at 80 - 120 °C, and the baking time is 4 - 8H.

[0026] The beneficial effects of the present invention are as follows:

[0027] 1. The anisotropic insulating and heat-conducting sheet material of the present invention at least includes a flexible polymer material, carbon fiber, spherical micropowder, and a flame retardant, so that irregular heat-conducting fillers are mixed in the thermosetting flexible polymer material, and the fibrous heat-conducting fillers are oriented in the flow direction, which is a heat-conducting sheet material with excellent heat-conducting performance and insulating performance;

[0028] 2. The preparation method of the present invention utilizes the shearing force to make the fibrous heat-conducting fillers oriented in the flow direction, so that the heat-conducting pre-material has good heat-conducting performance in the flow velocity direction after heating and curing, and an insulating and heat-conducting sheet material with carbon fibers oriented in the thickness direction is obtained by slicing. Specific Embodiments

[0029] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0030] An anisotropic insulating and heat-conducting sheet material, including a heat-conducting sheet material, and the raw materials for preparing the anisotropic insulating and heat-conducting sheet material at least include a flexible polymer material, carbon fiber, spherical micropowder, and a flame retardant, and the carbon fibers are oriented in the thickness direction of the heat-conducting sheet material.

[0031] As a further solution, the raw materials of the present invention at least include 150 - 300 parts by weight of a flexible polymer material, 500 - 800 parts by weight of carbon fiber, 1200 - 1800 parts by weight of spherical micropowder, and 150 - 200 parts by weight of a flame retardant.

[0032] As a further solution, the flexible polymer material of the present invention can be selected but is not limited to one or more mixtures of liquid acrylic resin, epoxy resin, polyurethane resin, unsaturated polyester resin, and silicone resin. Preferably, silicone resin is selected. The flame retardant is one or more mixtures of aluminum hydroxide, magnesium hydroxide, phosphorus-based flame retardant, and antimony trioxide. In the present invention, aluminum hydroxide is preferably used, and the average particle size of aluminum hydroxide is 0.1 - 5 μm.

[0033] As a further solution, the raw materials of the present invention further include 100 - 150 parts by weight of vinyl silicone oil, and the viscosity of the vinyl silicone oil is 500 - 100000 mPa·s.

[0034] As a further solution, the raw materials of the present invention further include 80-120 parts by weight of dimethyl silicone oil, 0.05-0.2 parts by weight of delay inhibitor, 3-6 parts by weight of H-containing silicone oil, and 1-3 parts by weight of platinum water catalyst.

[0035] As a further solution, the spherical micropowder of the present invention is a compound powder containing alumina and silicate powder, and the average particle size of the spherical micropowder is 0.1-5 μm. Preferably, the spherical micropowder further contains one or more mixtures of a small amount of boron nitride, aluminum nitride, and silicon carbide.

[0036] As a further preferred solution, the carbon fiber of the present invention is one of polyacrylonitrile-based carbon fiber, pitch-based carbon fiber, viscose-based carbon fiber, phenolic-based carbon fiber, and vapor-grown carbon fiber with a surface insulation coating. The average diameter of the carbon fiber is 2-30 μm, and the length is 50-300 μm.

[0037] The surface insulation coating process of the carbon fiber adopted in the present invention is as follows:

[0038] Carbon fiber surface activation step: Heat-treat the surface of the carbon fiber substrate using a muffle furnace at 500-1000 °C for 10 h to enhance the activity of the carbon fiber substrate surface and obtain activated carbon fiber;

[0039] Step of forming an insulation coating: Mix the above-activated carbon fiber with tetraethyl orthosilicate, ethanol, and a catalyst according to 30-100 g of carbon fiber, 5-200 ml of tetraethyl orthosilicate, 100-500 ml of ethanol, and 10-100 ml of 10% ammonium hydroxide solution, heat to 50 °C on a heating table, stir and mix evenly, so that a uniform and stable SiO2 insulation coating is gradually formed on the surface of the carbon fiber, and SiO2-insulated carbon fiber is obtained after suction filtration;

[0040] Baking step: Transfer the above-insulated carbon fiber to an oven for baking.

[0041] In the above baking step, segmented baking is adopted. The baking temperature in the first stage is 50-120 °C, and the time is 1-3 h, preferably 100 °C; the baking temperature in the second stage is 200-300 °C, and the baking time is 2-4 h, preferably 250 °C.

[0042] As a further solution, a polymer coating is formed on the surface of the heat-conducting sheet material of the present invention by coating a polymer coating. The polymer coating includes 80-120 parts by weight of vinyl silicone oil, 40-65 parts by weight of dimethyl silicone oil, 0.05-0.2 parts by weight of a delay inhibitor, 2-5 parts by weight of H-containing silicone oil, 1-3 parts by weight of a platinum water catalyst, and 150-200 parts by weight of long-chain alkyl siloxane. The long-chain alkyl siloxane added to the polymer coating has the effect of volatilizing when heated, which is beneficial to increasing the viscosity of the polymer coating. Further, in order to obtain a better heat-conducting effect, a small amount of spherical micropowder can also be added to the polymer coating. The specific addition amount is 200-450 parts by weight, and the average particle size of the spherical micropowder is 0.1-5 μm.

[0043] As a further solution, the thickness of the polymer coating of the present invention is ≤50 μm.

[0044] The present invention also provides a preparation method of an anisotropic insulating and heat-conducting sheet material. By using the action of shear force, fibrous heat-conducting fillers are oriented in the flow velocity direction to obtain an anisotropic insulating and heat-conducting sheet material with excellent performance.

[0045] A preparation method of an anisotropic insulating and heat-conducting sheet material includes

[0046] The step of preparing a heat-conducting pre-material: uniformly mixing carbon fiber, spherical micropowder and a flame retardant in a flexible polymer material to prepare a heat-conducting pre-material;

[0047] The flow velocity shear orientation step: the above heat-conducting pre-material is extruded through an extruder to orient the carbon fiber in the flow velocity direction, and is heated and cured in a movable die groove that can be clamped to form a formed body;

[0048] The ultrasonic cutting step: the above formed body is cut by ultrasonic cutting along the direction perpendicular to the flow velocity to obtain a heat-conducting sheet material with carbon fiber oriented along the thickness direction.

[0049] As a further solution, the preparation method of the present invention further includes a surface treatment step of the heat-conducting sheet material. The surface treatment of the heat-conducting sheet material is to form a polymer coating on the surface of the heat-conducting sheet by coating a polymer coating or to polish the surface of the heat-conducting sheet to make it smooth.

[0050] As a further solution, in the preparation method of the present invention, after the step of preparing the heat-conducting pre-material and before the flow velocity shear orientation step, it further includes the step of placing the uniformly mixed heat-conducting pre-material in a vacuum box for vacuum pumping. The vacuum degree of the vacuum box is ≤-0.09 Mpa, and the vacuum pumping time is ≥8 min.

[0051] As a further solution, release films are pasted around the die device of the present invention.

[0052] As a further solution, the extruder described in the present invention is a screw extruder, and the extrusion nozzle of the extruder is a honeycomb extrusion nozzle; the cross-sectional area of a single pore in the honeycomb extrusion nozzle ≤ 81 mm 2 , the wall thickness ≤ 0.1 mm, and the length of the honeycomb extrusion nozzle ≥ 5 cm.

[0053] As a further solution, the extrusion flow channel of the extruder described in the present invention is a conical flow channel. At least one flow dividing device is installed at the connection of the conical flow channel and the honeycomb extrusion nozzle. The end of the honeycomb extrusion nozzle is connected to the movable mold groove that can be clamped. A limiter for controlling the backward movement distance of the mold groove is installed at the end of the movable mold groove.

[0054] As a further solution, in the flow velocity shear orientation step described in the present invention, hot air curing is adopted in a blast oven. The temperature of the oven is set at 80 - 120 °C, and the baking time is 4 - 8 h.

[0055] Furthermore, in the ultrasonic cutting step, the vibration frequency of the ultrasonic cutting machine > 20 KHz, and the downward movement speed of the tool holder < 10 mm / min.

[0056] The following are specific embodiments of the present invention. In the following embodiments, the raw materials, equipment, etc. can be obtained by purchasing, except for those specifically defined in the present invention.

[0057] In the following embodiments, the carbon fiber adopted in the present invention is obtained by the following method:

[0058] Carbon fiber surface activation step: The surface of the carbon fiber substrate is heat-treated using a muffle furnace at 500 °C for 12 h to enhance the activity of the carbon fiber substrate surface, obtaining activated carbon fiber;

[0059] Step of forming an insulating coating: Weigh 50 g of the above carbon fiber and place it in a beaker. Measure 80 ml of tetraethyl orthosilicate and 400 ml of absolute ethanol. Pour tetraethyl orthosilicate and absolute ethanol into the beaker through the guiding action of a glass rod, and stir with a stirring paddle. The stirring process is carried out on a heating platform with the temperature of the heating platform set at 50 °C, the stirring speed at 1500 rpm, and the stirring time at 4 h. When the carbon fiber is evenly mixed in the solution, add ammonia water as a catalyst using a dropper. The addition amount of ammonia water is 100 ml, and the dropping time is controlled within 40 min. During the stirring process, the pH value of the solution is maintained at about 10. When the pH value is greater than 10, add acetic acid for adjustment. After the stirring is completed, filter the carbon fiber mixed solution using a vacuum filtration device. During the filtration process, continuously add ethanol solution to wash the carbon fiber until the solution after filtration is neutral, obtaining carbon fiber insulated and coated with SiO2;

[0060] Baking step: Transfer the above-mentioned carbon fiber insulated and coated with SiO2 to an oven for baking. Segmented baking is adopted. In the first stage, it is placed in an oven with a temperature set at 50 °C and baked for 3 hours to remove ethanol and moisture attached to the carbon fiber. In the second stage, it is placed in a muffle furnace for calcination. The temperature is set at 300 °C and the calcination time is 2 hours to form a dense and stable SiO2 insulating coating on the surface of the carbon fiber.

[0061] Example 1

[0062] An anisotropic insulating and heat-conducting sheet, including a heat-conducting sheet. A polymer coating is formed on the surface of the heat-conducting sheet by coating a polymer coating. The raw materials for preparing the anisotropic insulating and heat-conducting sheet at least include a flexible polymer material, carbon fiber, spherical micropowder, and a flame retardant. The carbon fiber is oriented in the thickness direction of the heat-conducting sheet;

[0063] The preparation method is as follows:

[0064] Steps for preparing a heat-conducting preform: Mix 15 parts by weight of methyl vinyl silicone rubber, 100 parts by weight of vinyl silicone oil with a viscosity of 800 mpa.s, 80 parts by weight of dimethyl silicone oil, 3 parts by weight of hydrogen-containing silicone oil, 1 part by weight of platinum water catalyst, 1200 parts by weight of spherical micropowder, 150 parts by weight of aluminum hydroxide, and 500 parts by weight of carbon fiber evenly by open milling to obtain a heat-conducting preform;

[0065] Flow velocity shear orientation step: Place the uniformly mixed heat-conducting preform in a vacuum box with a vacuum degree of -0.09 Mpa and evacuate for 10 minutes. Orient the carbon fiber in the flow velocity direction by extrusion through an extruder. The extrusion speed is less than 20 rpm / min, and it is heated to 80 °C for curing in a movable die groove that can be clamped to form a formed body. The extruder is a screw extruder, and the extrusion nozzle of the extruder is a honeycomb extrusion nozzle; the single pore area of the honeycomb extrusion nozzle in the honeycomb extrusion nozzle is 10 mm 2 , with a length of 10 cm and a wall thickness of 0.1 mm;

[0066] Ultrasonic cutting step: Cut the above-mentioned formed body by ultrasonic cutting along the direction perpendicular to the flow velocity intersection to obtain a heat-conducting sheet with carbon fiber oriented in the thickness direction. The vibration frequency of the ultrasonic cutting machine is 25 KHz, and the downward movement speed of the tool holder is 8 mm / min;

[0067] Steps for coating with a polymer coating: Stir 80 parts by weight of vinyl silicone oil, 40 parts by weight of dimethyl silicone oil, 0.05 part by weight of a delay inhibitor, 2 parts by weight of H-containing silicone oil, 1 part by weight of a platinum water catalyst, and 150 parts by weight of long-chain alkyl siloxane evenly to obtain a polymer coating. Use a coater to evenly coat the polymer coating on the heat-conducting sheet material, with the coating thickness less than 50 μm. Then put it into an oven at 150 °C and heat for 10 min for curing to obtain a heat-conducting sheet material with a sticky surface.

[0068] Example 2

[0069] An anisotropic insulating and heat-conducting sheet material includes a heat-conducting sheet material. A polymer coating is formed on the surface of the heat-conducting sheet material by coating with a polymer coating. The raw materials for preparing the anisotropic insulating and heat-conducting sheet material at least include a flexible polymer material, carbon fiber, spherical micropowder, and a flame retardant. The carbon fiber is oriented in the thickness direction of the heat-conducting sheet material;

[0070] Its preparation method is as follows:

[0071] Steps for preparing a heat-conducting preliminary material: Mix 15 parts by weight of methyl vinyl silicone rubber, 150 parts by weight of vinyl silicone oil with a viscosity of 100000 mPa·s, 120 parts by weight of dimethyl silicone oil, 0.08 part by weight of a delay inhibitor, 4.0 parts by weight of H-containing silicone oil, 3 parts by weight of a platinum water catalyst, 1200 parts by weight of spherical micropowder, 150 parts by weight of aluminum hydroxide, and 850 parts by weight of carbon fiber evenly by open milling to obtain a heat-conducting preliminary material;

[0072] Flow velocity shear orientation step: Place the evenly mixed heat-conducting preliminary material in a vacuum box with a vacuum degree of -0.09 Mpa and evacuate for 10 min. Orient the carbon fiber in the flow velocity direction by extrusion through an extruder, with the extrusion speed less than 20 rpm / min, and heat and cure to 80 °C in a movable mold groove that can be closed to form a molded body. The extruder is a screw extruder, and the extrusion nozzle of the extruder is a honeycomb extrusion nozzle; the single pore area of the honeycomb extrusion nozzle in the honeycomb extrusion nozzle is 10 mm 2 , with a length of 10 cm and a wall thickness of 0.1 mm;

[0073] Ultrasonic cutting step: Cut the above-mentioned molded body by ultrasonic cutting along the direction perpendicular to the flow velocity intersection to obtain a heat-conducting sheet material with carbon fiber oriented in the thickness direction. The vibration frequency of the ultrasonic cutting machine is 25 KHz, and the downward movement speed of the tool holder is 8 mm / min;

[0074] Steps for coating with a polymer coating: Stir 120 parts by weight of vinyl silicone oil, 65 parts by weight of dimethyl silicone oil, 0.05 part by weight of delay inhibitor, 5 parts by weight of H-containing silicone oil, 3 parts by weight of platinum water catalyst, and 200 parts by weight of long-chain alkyl siloxane evenly to obtain a polymer coating material. Use a coater to evenly coat the polymer coating material on the heat-conducting sheet, with the coating thickness less than 50 μm. Then put it into an oven at 150 °C and heat for 10 min for curing to obtain a heat-conducting sheet with a sticky surface.

[0075] Example 3

[0076] On the basis of Example 1, replace the step of coating with a polymer coating with polishing the surface of the heat-conducting sheet smoothly. The surface polishing methods are not limited to sand polishing, polishing machine polishing, kraft paper polishing, silicon carbide ceramic large-pore grinding wheel, etc.

[0077] Example 4

[0078] On the basis of Example 1, use vinyl silicone oil with a viscosity of 10,000 mPa·s to adjust the overall viscosity of the heat-conducting pre-material, and operate through the same steps as in Example 1 to obtain a heat-conducting sheet.

[0079] Examples 5 - 8

[0080] On the basis of Example 1, adjust the single pore area of the honeycomb extrusion nozzle, and obtain a heat-conducting sheet according to the same operation steps as in Example 1. The single pore areas of the honeycomb extrusion nozzles used in Examples 5 - 8 are 4 mm 2 、8 mm 2 、30 mm 2 、60 mm 2 .

[0081] Examples 9 - 12

[0082] On the basis of Example 1, adjust the thickness of the surface polymer coating, and obtain a heat-conducting sheet according to the same operation steps as in Example 1. The thicknesses of the polymer coatings in Examples 9 - 12 are 20 μm, 30 μm, 80 μm, and 110 μm respectively.

[0083] Detect the performance of the heat-conducting sheets of the above Examples 1 - 12 respectively. The detection items include thermal conductivity, hardness, breakdown voltage, and surface adhesiveness. See Table 1 for specific results.

[0084] Table 1: Performance comparison of the heat-conducting sheets of Examples 1 - 12

[0085]

[0086]

[0087] The following conclusions can be drawn from the results in Table 1

[0088] 1) From the results of the thermal conductivity of the finally obtained thermally conductive sheet, it can be seen that the smaller the viscosity of the prepreg, the more beneficial it is for the carbon fiber to orient in the flow direction, thereby obtaining a higher thermal conductivity. When vinyl silicone oil with a viscosity of 10,000 mPa·s is used, the thermal conductivity decreases due to the influence of the viscosity value.

[0089] 2) The amount of carbon fiber used will affect the orientation of the thermally conductive sheet. When the carbon fiber filling ratio increases, it also causes an increase in the overall viscosity of the prepreg, which instead hinders the orientation effect of the carbon fiber in the honeycomb extrusion nozzle.

[0090] 3) The area of a single pore of the honeycomb extrusion nozzle will affect the thermal conductivity of the thermally conductive sheet. Specifically, when the area of a single pore of the honeycomb extrusion nozzle < 10 mm 2 , observed with a 2.5D imaging instrument, the overall arrangement of the carbon fiber is good, and the influence on the thermal conductivity is not significant; when the area of a single pore of the honeycomb extrusion nozzle > 50 mm 2 , observed with a 2.5D imaging instrument, only the carbon fiber at the wall-attached part is arranged neatly along the flow direction, and the arrangement of the carbon fiber becomes more chaotic towards the center part, and the thermal conductivity decreases to varying degrees.

[0091] 4) The thickness of the polymer coating on the surface of the thermally conductive sheet also affects the thermal conductivity. Specifically, when the surface coating thickness is less than 50 μm, the influence on the thermal conductivity is not significant; when the coating thickness > 100 μm, the thermal conductivity of the thermally conductive sheet drops sharply.

[0092] The above has introduced in detail an anisotropic insulating thermally conductive sheet provided by the embodiments of the present invention. Specific examples are used in this article to elaborate on the principle and implementation manner of the present invention. The description of the above embodiments is only used to help understand the core idea of the present invention; at the same time, for those of ordinary skill in the art, according to the idea and method of the present invention, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation to the present invention.

Claims

1. An anisotropic insulating and heat-conductive sheet, comprising a heat-conductive sheet, characterized in that, The raw materials for preparing the anisotropic insulating and heat-conducting sheet at least include 150-300 parts by weight of a flexible polymer material, 500-800 parts by weight of carbon fiber, 1200-1800 parts by weight of spherical micropowder, and 150-200 parts by weight of a flame retardant. It also includes 100-150 parts by weight of vinyl silicone oil with a viscosity of 500-10000 mPa·s. A polymer coating is formed on the surface of the heat-conducting sheet by coating a polymer coating. The polymer coating includes, by weight, 80-120 parts of vinyl silicone oil, 40-65 parts of dimethyl silicone oil, 0.05-0.2 parts by weight of a delay inhibitor, 2-5 parts of H-containing silicone oil, 1-3 parts of a platinum water catalyst, and 150-200 parts of long-chain alkyl siloxane. The carbon fiber is oriented in the thickness direction of the heat-conducting sheet. The heat-conducting sheet is connected to the mold cavity of the movable mold that can be closed at the end of the extruder. The carbon fiber is oriented in the flow rate direction by extrusion through the extruder, and is heated and cured in the mold cavity of the movable mold that can be closed to form a molded body. The above molded body is cut by ultrasonic cutting along the direction perpendicular to the flow rate to obtain a heat-conducting sheet with carbon fiber oriented in the thickness direction. The extruder is a screw extruder, and the extrusion nozzle of the extruder is a honeycomb extrusion nozzle. The cross-sectional area of a single pore in the honeycomb extrusion nozzle ≤ 60 mm 2 , the wall thickness ≤ 0.1 mm, and the length of the honeycomb extrusion nozzle ≥ 5 cm. The extrusion channel of the extruder is a conical channel. At least one flow dividing device is installed at the connection between the conical channel and the honeycomb extrusion nozzle. The end of the honeycomb extrusion nozzle is connected to the mold cavity of the movable mold that can be closed, and a limiter for controlling the backward movement distance of the mold cavity is installed at the end of the movable mold cavity; The carbon fiber is one of polyacrylonitrile-based carbon fiber, pitch-based carbon fiber, viscose-based carbon fiber, phenolic-based carbon fiber, and vapor-grown carbon fiber with a surface insulation coating; The thickness of the polymer coating is ≤ 50 μm.

2. The anisotropic insulating and heat-conductive sheet according to claim 1, wherein The flexible polymer material is one or a mixture of two or more of liquid acrylic resin, epoxy resin, polyurethane resin, unsaturated polyester resin, and silicone resin.

3. The anisotropic insulating and heat-conductive sheet according to claim 2, characterized in that, The raw materials further include 80 - 120 parts by weight of dimethyl silicone oil, 0.05 - 0.2 parts by weight of a delay inhibitor, 3 - 6 parts by weight of H-containing silicone oil, and 1 - 3 parts by weight of a platinum water catalyst.

4. The anisotropic insulating and heat-conductive sheet according to any one of claims 2-3, characterized in that The spherical fine powder is a compound powder containing alumina and silicate powder, and the average particle size of the spherical fine powder is 0.1 - 5 μm.

5. The anisotropic insulating and heat-conductive sheet according to any one of claims 1 to 3, characterized in that, The average diameter of the carbon fiber is 2 - 30 μm, and the length is 50 - 300 μm.

6. A method for preparing an anisotropic insulating and heat-conducting sheet as described in claim 1, characterized in that, Including Steps for preparing a heat-conductive preform: uniformly mixing carbon fiber, spherical fine powder, and a flame retardant in a flexible polymer material to prepare a heat-conductive preform; Flow velocity shear orientation step: The above-mentioned thermal conductivity prepreg is extruded through an extruder to orient the carbon fibers in the flow velocity direction, and is heated and cured in a movable mold groove that can be closed to form a molded body. The extruder is a screw extruder, and the extrusion nozzle of the extruder is a honeycomb extrusion nozzle; the cross-sectional area of a single pore in the honeycomb extrusion nozzle ≤ 60 mm 2 , the wall thickness ≤ 0.1 mm, and the length of the honeycomb extrusion nozzle ≥ 5 cm; the extrusion channel of the extruder is a conical channel, and at least one flow splitting device is installed at the connection between the conical channel and the honeycomb extrusion nozzle. The end of the honeycomb extrusion nozzle is connected to the movable mold groove that can be closed, and a stopper for controlling the backward movement distance of the mold groove is installed at the end of the movable mold groove; Ultrasonic cutting step: cutting the above-mentioned formed body by ultrasonic cutting along the direction perpendicular to the flow velocity intersection direction to obtain a heat-conductive sheet with carbon fibers oriented along the thickness direction.

7. The preparation method according to claim 6, characterized in that, After the step of preparing the heat-conductive preform and before the flow velocity shear orientation step, there is also a step of placing the uniformly mixed heat-conductive preform in a vacuum chamber for vacuum pumping. The vacuum degree of the vacuum chamber is ≤ -0.09 Mpa, and the vacuum pumping time is ≥ 8 min.

8. The preparation method according to claim 6, characterized in that, Release films are pasted around the mold device.

9. The preparation method according to claim 7, wherein In the flow velocity shear orientation step, heating and curing are carried out using a forced-air oven. The temperature of the oven is set at 80 - 120 °C, and the baking time is 4 - 8 h.

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