A heat dissipation film for a mobile phone battery protection circuit and a preparation method thereof

Abstract

The application discloses a heat dissipation film for a mobile phone battery protection circuit and a preparation method thereof, and the preparation method comprises the following steps: S1, carrying out two-dimensional treatment on hexagonal boron nitride raw materials to obtain hexagonal boron nitride sheets with different sheet diameters; the two-dimensional treatment adopts a high-energy sand grinding stripping method, and the interlayer force of the hexagonal boron nitride is destroyed through solvent molecular intercalation; S2, mixing the hexagonal boron nitride sheets with different diameter-thickness ratios and different sheet diameters obtained in the step S1 with a bonding resin, a dispersing agent and an organic solvent, and adding a puncture-resistant reinforcing material to prepare a coating slurry; S3, adopting a doctor blade coating process to flow coating the coating slurry obtained in the step S2 on a substrate; and S4, carrying out segmented drying on the wet film after coating to obtain a dry film; through compounding of the hexagonal boron nitride with different sheet diameters, the powder gradation system is optimized, the slurry has stable thixotropic properties, and the stable ultra-thin film can be formed, and the film thickness uniformity is good.

Description

Technical Field

[0001] This invention relates to the field of heat dissipation technology for mobile phone battery protection circuits, and in particular to a heat dissipation film for mobile phone battery protection circuits and its preparation method. Background Technology

[0002] With the deep application of 5G mobile communication technology, artificial intelligence computing, and high-rate fast charging technology in smartphones, the power consumption of core components such as processors, power management chips, and battery protection circuit boards has significantly increased. This leads to a continuous increase in localized heat flux density within these components, making them prone to forming hot spots within the limited internal space of the device. If heat cannot be dissipated evenly and promptly, it will not only cause user experience issues such as processor throttling and system lag, but also accelerate the aging of circuit board components and solder joint failure under prolonged high temperatures. Furthermore, it will exacerbate battery surface temperature rise, increasing the safety risks of lithium battery bulging and thermal runaway. Therefore, the demand for high-performance insulating and heat-dissipating materials for the circuit boards and battery areas inside mobile phones is becoming increasingly urgent.

[0003] The highly integrated internal structure of current smartphones leaves extremely limited space for heat dissipation materials, typically only 30–1000 μm. Traditional metal heat sinks, due to their thickness and lack of insulation, cannot be directly applied to circuit board surfaces. While artificial graphite films, commonly used in the industry, possess high in-plane thermal conductivity, they suffer from low breakdown voltage and poor insulation stability, making them prone to insulation failure in densely traced areas of circuit boards. Furthermore, bending the material can generate debris, posing a risk of contaminating the circuit board and even causing short circuits. Traditional composite heat dissipation coatings using alumina and magnesium oxide as thermally conductive fillers often have equiaxed filler particles, resulting in a weak filler network structure and poor thixotropic properties. When preparing ultra-thin films of 30–1000 μm, filler sedimentation and poor film thickness uniformity are common problems, leading to low thermal conductivity in the final product, which fails to meet the heat dissipation requirements of high-power circuit boards.

[0004] The battery protection module (PCM) is a core component for battery safety. It is highly compact and operates in harsh environments. Core issues such as solder joint / pin puncture damage, high-temperature failure during fast charging, circuit insulation breakdown, insufficient vertical heat conduction, brittle fracture due to bending assembly, and electrolyte corrosion all require heat dissipation films to address.

[0005] Hexagonal boron nitride (BN) possesses high in-plane thermal conductivity, excellent electrical insulation, high-temperature resistance, and chemical stability, making it an ideal filler for preparing ultrathin insulating and heat-dissipating films. While existing BN heat-dissipating films have been gradually applied in the consumer electronics field, significant drawbacks remain: First, the aspect ratio of the boron nitride powder is not ideally matched, resulting in a low thixotropic coefficient in the slurry. In low-solids-content systems, the filler is prone to sedimentation, making it difficult to stably form ultrathin films of 30–1000 μm. Second, high-solids-content, high-thixotropic boron nitride slurries have poor fluidity, making it difficult to achieve ultrathin, uniform casting using conventional doctor blade coating processes. This results in poor film thickness consistency, failing to meet the thin-film assembly requirements of precision mobile phone circuit boards. Third, insufficient orientation of the boron nitride sheet within the film leads to lower-than-expected in-plane thermal conductivity, limiting its heat dissipation effect on localized hot spots such as MOSFETs and detection chips on circuit boards. Summary of the Invention

[0006] This invention addresses the shortcomings of existing boron nitride heat dissipation films, such as unreasonable powder gradation, poor thixotropic properties of the slurry, poor flowability due to high solid content, and low orientation of fillers inside the film. It provides a heat dissipation film for mobile phone battery protection circuits and its preparation method, achieving ultra-thin molding while ensuring uniform film thickness, high insulation, and high in-plane thermal conductivity. This makes it suitable for the precision assembly, high power consumption heat dissipation, puncture resistance, and high voltage resistance requirements of mobile phone battery protection circuit boards.

[0007] To achieve the above objectives, in a first aspect, the present invention adopts the following technical solution:

[0008] A method for preparing a heat dissipation film for a mobile phone battery protection circuit includes the following steps:

[0009] S1: The hexagonal boron nitride raw material is subjected to two-dimensional processing to obtain hexagonal boron nitride sheets with different aspect ratios and sheet diameters; the two-dimensional processing adopts a high-energy sand milling and exfoliation method, which destroys the interlayer forces of hexagonal boron nitride through solvent molecule intercalation;

[0010] S2: The hexagonal boron nitride sheets with different aspect ratios and sheet diameters obtained in step S1 are mixed with adhesive resin, dispersant and organic solvent, and puncture-resistant reinforcing material is added to prepare a coating slurry.

[0011] S3: Using a doctor blade coating process, the coating slurry obtained in step S2 is cast onto the substrate;

[0012] S4: Dry the coated wet film in stages to obtain a dry film;

[0013] S5: Cut and roll up the dried heat dissipation film.

[0014] Furthermore, the hexagonal boron nitride sheet includes at least two of the following: large-diameter hexagonal boron nitride sheet, medium-diameter hexagonal boron nitride sheet, and small-diameter hexagonal boron nitride sheet;

[0015] The aspect ratio of the large-diameter hexagonal boron nitride sheet is 60-120, and the sheet diameter is 5-20 μm;

[0016] The aspect ratio of the medium-diameter hexagonal boron nitride sheet is 40-80, and the sheet diameter is 2-8 μm;

[0017] The aspect ratio of the small-diameter hexagonal boron nitride sheet is 10 to 30, and the sheet diameter is 0.5 to 2 μm.

[0018] Furthermore, the solvent used in the sand milling and peeling method in step S1 is selected from one or more of N-methylpyrrolidone, N,N-dimethylformamide, isopropanol, or a combination of water and a surfactant.

[0019] Further, the bonding resin in step S2 is a thermoplastic polyurethane resin or an acrylic resin, and its addition amount accounts for 8% to 15% of the total mass of the slurry; the dispersant is one or more of aluminum metaphosphate or silicon pyrophosphate, and its addition amount is 1.5% to 3% of the total mass of the hexagonal boron nitride filler.

[0020] Furthermore, the puncture-resistant reinforcing material mentioned in step S2 is selected from one or more of glass fiber, aramid fiber, nano-silica, alumina, or silicon powder.

[0021] Furthermore, the preparation process of the coating slurry in step S2 includes: first stirring each component at a speed of 80-100 r / min for 20 minutes, and then increasing the speed to 450-550 r / min and stirring for 60 minutes.

[0022] Furthermore, in step S3, the blade gap in the blade coating process is 80–85 μm, and the coating speed is 3.5–4.0 m / min.

[0023] Furthermore, the coating slurry has a thixotropic coefficient of 2.2 to 3.5, a solid content of 40% to 90%, and a shear viscosity of 5000 to 20000 mPa·s.

[0024] Furthermore, the dry film thickness of the heat dissipation film is 30-1000 μm, the in-plane thermal conductivity is ≥70 W / (m·K), the breakdown voltage is ≥10 kV, and the number of folds without breakage is ≥10,000 under the condition of a radius of curvature of 5 mm.

[0025] Secondly, the present invention adopts the following technical solution:

[0026] A heat dissipation film for mobile phone battery protection circuit is prepared using the above-described method.

[0027] The beneficial effects of this invention include:

[0028] 1. This invention optimizes the powder gradation system by compounding hexagonal boron nitride with different flake sizes, so that the slurry has stable thixotropic properties, can stably form ultra-thin films, and has good film thickness uniformity.

[0029] 2. This invention performs two-dimensional processing on hexagonal boron nitride using a sand milling and peeling method, and adds aluminum metaphosphate and silicon pyrophosphate to adjust the inter-layer potential and reduce agglomeration, thereby achieving highly oriented and dense stacking of boron nitride layers, constructing an efficient in-plane thermal conductivity network, and significantly improving the in-plane thermal conductivity.

[0030] 3. This invention, by adding high-strength rigid fillers such as alumina as puncture-resistant reinforcing materials, forms a physical barrier layer in the boron nitride matrix, which greatly improves the puncture resistance and bending reliability of the heat dissipation film. It effectively solves the problems of high brittleness, easy slippage of sheets, easy cracking and powdering during bending, and easy breakage during hot pressing and assembly of pure boron nitride films, thus meeting the assembly and use requirements of mobile phone battery protection circuit boards.

[0031] 4. This invention employs a doctor blade coating process with a doctor blade gap of 80-85 μm and a coating speed of 3.5-4.0 m / min, achieving ultra-thin and uniform casting of high solids content and high thixotropic boron nitride slurry, effectively solving the problems of stripe defects and uneven film layer that are prone to occur in conventional low-speed coating processes. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. The term "and / or" as used herein includes all and any combination of one or more of the associated listed items.

[0034] Example 1

[0035] A method for preparing a heat dissipation film for a mobile phone battery protection circuit includes the following steps:

[0036] S1. Two-dimensional processing of hexagonal boron nitride sheets:

[0037] Preparation of large-diameter hexagonal boron nitride sheets:

[0038] Weigh out 15% hexagonal boron nitride powder, 84% dispersion medium (N-methylpyrrolidone:N,N-dimethylformamide in a 7:3 ratio), and dispersant (polyacrylate) according to the following mass ratio. Add the above materials together with zirconia beads (1.2–1.5 mm particle size) into a sand mill. Set the milling speed to 1200–1400 r / min and circulate the mill for 2.5–3 hours, controlling the slurry temperature below 55℃. After milling, pass the slurry through a 1000-mesh sieve and vacuum dry to obtain large-diameter hexagonal boron nitride sheets. The aspect ratio of these large-diameter hexagonal boron nitride sheets is 60–120, and the sheet diameter is 5–20 μm.

[0039] Preparation of small-diameter hexagonal boron nitride sheets:

[0040] Weigh out 12% hexagonal boron nitride powder, 87% dispersion medium (N-methylpyrrolidone), and 1% dispersant (polyacrylate) according to the following mass ratio. Add the above materials together with zirconia beads (0.4–0.6 mm particle size) into a sand mill. Set the milling speed to 2200–2400 r / min and circulate the mill for 4–5 hours, controlling the slurry temperature below 50℃. After milling, pass the slurry through a 3000-mesh sieve and dry it to obtain small-diameter hexagonal boron nitride flakes. The aspect ratio of these small-diameter hexagonal boron nitride flakes is 10–30, and the flake diameter is 0.5–2 μm.

[0041] S2. Slurry preparation:

[0042] Take 85 parts of the large-diameter hexagonal boron nitride and 15 parts of the small-diameter hexagonal boron nitride prepared above, add 2 parts of alumina, 12 parts of acrylic resin, 1.5 parts of aluminum metaphosphate, and 0.5 parts of silicon pyrophosphate, and then add ethyl acetate to dissolve and disperse the components. Stir at 80–100 r / min for 20 minutes, then increase the speed to 450–550 r / min and stir for 60 minutes to obtain the coating slurry. The thixotropic coefficient of the coating slurry is 2.2–3.5, the solid content is 40%–90%, and the shear viscosity is 5000–20000 mPa·s.

[0043] S3, Cast coating:

[0044] The blade coating process was adopted, with the blade gap set at 80μm, the coating speed at 3.5m / min, and the coating temperature at 12℃, to cast the coating slurry onto the substrate.

[0045] S4. Segmented drying:

[0046] The coated wet film was dried in stages at three temperature ranges: 60℃, 90℃, and 120℃.

[0047] S5. Slitting and winding:

[0048] The dried and shaped heat dissipation film was slit and rolled up to obtain a hexagonal boron nitride heat dissipation film with a dry film thickness of 35 μm.

[0049] The thermal conductivity of the heat dissipation film prepared in this embodiment is 75 W / (m·K), the breakdown voltage is greater than 14 kV, the film thickness deviation is ±2 μm, and the number of folds without breakage under a curvature radius of 5 mm is greater than 10,000.

[0050] Example 2

[0051] A method for preparing a heat dissipation film for a mobile phone battery protection circuit includes the following steps:

[0052] S1. Two-dimensional processing of hexagonal boron nitride sheets:

[0053] Similar to Example 1, large-diameter hexagonal boron nitride sheets and small-diameter hexagonal boron nitride sheets were prepared respectively.

[0054] S2. Slurry preparation:

[0055] Take 90 parts of large-diameter hexagonal boron nitride and 10 parts of small-diameter hexagonal boron nitride, add 2 parts of alumina, 10 parts of polyurethane resin, 1.7 parts of aluminum metaphosphate, and 0.8 parts of silicon pyrophosphate, then add ethyl acetate to dissolve and disperse the components. Stir at 80–100 r / min for 20 minutes, then increase the speed to 450–550 r / min and stir for 60 minutes to obtain the coating slurry. The thixotropic coefficient of the coating slurry is 2.2–3.5, the solid content is 40%–90%, and the shear viscosity is 5000–20000 mPa·s.

[0056] S3, Cast coating:

[0057] The coating process is adopted, with the blade gap set at 85μm and the coating speed at 4.0m / min, and the coating slurry is cast onto the substrate.

[0058] S4. Segmented drying:

[0059] The coated wet film was dried in stages at three temperature ranges: 60℃, 90℃, and 120℃.

[0060] S5. Slitting and winding:

[0061] The dried and shaped heat dissipation film was slit and rolled up to obtain a hexagonal boron nitride heat dissipation film with a dry film thickness of 38 μm.

[0062] The thermal conductivity of the heat dissipation film prepared in this embodiment is 80 W / (m·K), the breakdown voltage is greater than 14 kV, the film thickness deviation is ±2 μm, and the number of folds without breakage under a curvature radius of 5 mm is greater than 10,000.

[0063] Example 3

[0064] A method for preparing a heat dissipation film for a mobile phone battery protection circuit includes the following steps:

[0065] S1. Two-dimensional processing of hexagonal boron nitride sheets:

[0066] Preparation of large-diameter hexagonal boron nitride sheets:

[0067] Same as Example 1.

[0068] Preparation of medium-diameter hexagonal boron nitride sheets:

[0069] Weigh out 18% hexagonal boron nitride powder, 81% dispersion medium (N-methylpyrrolidone:N,N-dimethylformamide in a 7:3 ratio), and 1% dispersant (polyacrylate) according to the following mass ratio. Add the above materials together with zirconia beads (1.2–1.5 mm particle size) into a sand mill. Set the milling speed to 1500–1700 r / min and circulate the mill for 3.5 hours, controlling the slurry temperature below 55℃. After milling, pass the slurry through a 2000-mesh sieve and vacuum dry to obtain medium-diameter hexagonal boron nitride flakes. The diameter of these medium-diameter hexagonal boron nitride flakes is 2–8 μm.

[0070] Preparation of small-diameter hexagonal boron nitride sheets:

[0071] Same as Example 1.

[0072] S2. Slurry preparation:

[0073] Take 65 parts of large-diameter hexagonal boron nitride, 20 parts of medium-diameter hexagonal boron nitride, and 15 parts of small-diameter hexagonal boron nitride. Add 2 parts of alumina, 10 parts of polyurethane resin, 1.7 parts of aluminum metaphosphate, and 0.8 parts of silicon pyrophosphate. Then add ethyl acetate to dissolve and disperse the components. Stir at 80-100 r / min for 20 minutes, then increase the speed to 450-550 r / min and stir for 60 minutes to obtain the coating slurry. The thixotropic coefficient of the coating slurry is 2.2-3.5, the solid content is 40%-90%, and the shear viscosity is 5000-20000 mPa·s.

[0074] S3, Cast coating:

[0075] The coating process is adopted, with the blade gap set at 85μm and the coating speed at 4.0m / min, and the coating slurry is cast onto the substrate.

[0076] S4. Segmented drying:

[0077] The coated wet film was dried in stages at three temperature ranges: 60℃, 90℃, and 120℃.

[0078] S5. Slitting and winding:

[0079] The dried and shaped heat dissipation film was slit and rolled up to obtain a hexagonal boron nitride heat dissipation film with a dry film thickness of 38 μm.

[0080] The thermal conductivity of the heat dissipation film prepared in this embodiment is 86 W / (m·K), the breakdown voltage is greater than 15 kV, the film thickness deviation is ±2 μm, and the number of folds without breakage under a curvature radius of 5 mm is greater than 10,000.

[0081] Comparative Example 1

[0082] A single hexagonal boron nitride filler with a diameter-to-thickness ratio of 70 was used, without mixing large and small sheet diameters, and the other preparation conditions were the same as in Example 1.

[0083] During the coating process, significant sedimentation of the slurry occurred, resulting in a large deviation in film thickness. Testing revealed that the surface thermal conductivity of the obtained heat dissipation film was only 8.3 W / (m·K), which fails to meet the application requirements.

[0084] Comparative Example 2

[0085] The conventional low-speed coating process was used, and the remaining preparation conditions were the same as in Example 1.

[0086] Due to the poor fluidity of the slurry, stripe defects appear during the coating process, resulting in poor film uniformity and making it impossible to obtain a heat dissipation film with uniform thickness.

[0087] Comparative Example 3

[0088] The formulation of Example 3 was used, but only small-diameter hexagonal boron nitride was added, and large-diameter hexagonal boron nitride, medium-diameter hexagonal boron nitride, aluminum metaphosphate and silicon pyrophosphate were not added. The other preparation conditions were the same as in Example 3.

[0089] Testing revealed that the thermal conductivity of the prepared heat dissipation film was only 32 W / (m·K), and the breakdown voltage was greater than 3.5 kV, which did not meet the usage requirements.

[0090] As can be seen from Examples 1-3, the hexagonal boron nitride heat dissipation film prepared using the technical solution of the present invention has an in-plane thermal conductivity of 75-86 W / (m·K), a breakdown voltage greater than 14kV, a film thickness deviation controlled within ±2μm, and a bending reliability greater than 10,000 times, which fully meets the heat dissipation, insulation and assembly requirements of mobile phone battery protection circuit boards.

[0091] The comparison between Example 1 and Comparative Example 1 shows that when using a single boron nitride filler with a diameter-to-thickness ratio, the slurry settles severely, and the thermal conductivity drops sharply to 8.3 W / (m·K). This indicates that the compound system of two boron nitride fillers with large and small diameters in this invention can improve the stability and thermal conductivity of the slurry.

[0092] As can be seen from the comparison between Example 1 and Comparative Example 2, when using the conventional low-speed coating process, due to the mismatch with the thixotropic properties of the slurry, stripe defects appear in the coating and the film uniformity is poor.

[0093] The comparison between Example 3 and Comparative Example 3 shows that when only small-diameter boron nitride is added and aluminum metaphosphate and silicon pyrophosphate are not added, the thermal conductivity is only 32 W / (m·K) and the breakdown voltage is only greater than 3.5 kV. This indicates that the composite system of three types of boron nitride with large, medium and small diameters, as well as the addition of aluminum metaphosphate and silicon pyrophosphate, have a significant synergistic effect on improving thermal conductivity and insulation performance.

[0094] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. 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 present invention.

Claims

1. A method for preparing a heat dissipation film for a mobile phone battery protection circuit, characterized in that, Includes the following steps: S1: The hexagonal boron nitride raw material is subjected to two-dimensional processing to obtain hexagonal boron nitride sheets with different aspect ratios and sheet diameters; the two-dimensional processing adopts a high-energy sand milling and exfoliation method, which destroys the interlayer forces of hexagonal boron nitride through solvent molecule intercalation; S2: The hexagonal boron nitride sheets with different aspect ratios and sheet diameters obtained in step S1 are mixed with adhesive resin, dispersant and organic solvent, and puncture-resistant reinforcing material is added to prepare a coating slurry. S3: Using a doctor blade coating process, the coating slurry obtained in step S2 is cast onto the substrate; S4: Dry the coated wet film in stages to obtain a dry film; S5: Cut and roll up the dried heat dissipation film.

2. The preparation method according to claim 1, characterized in that, In step S1, the hexagonal boron nitride sheet includes at least two of the following: large-diameter hexagonal boron nitride sheet, medium-diameter hexagonal boron nitride sheet, and small-diameter hexagonal boron nitride sheet; The aspect ratio of the large-diameter hexagonal boron nitride sheet is 60-120, and the sheet diameter is 5-20 μm; The aspect ratio of the medium-diameter hexagonal boron nitride sheet is 40-80, and the sheet diameter is 2-8 μm; The aspect ratio of the small-diameter hexagonal boron nitride sheet is 10 to 30, and the sheet diameter is 0.5 to 2 μm.

3. The preparation method according to claim 1, characterized in that, The solvent used in the sand milling and peeling method in step S1 is selected from one or more of N-methylpyrrolidone, N,N-dimethylformamide, isopropanol, or a combination of water and surfactant.

4. The preparation method according to claim 1, characterized in that, The bonding resin mentioned in step S2 is a thermoplastic polyurethane resin or an acrylic resin, and its addition amount accounts for 8% to 15% of the total mass of the slurry; the dispersant is one or more of aluminum metaphosphate or silicon pyrophosphate, and its addition amount is 1.5% to 3% of the total mass of the hexagonal boron nitride filler.

5. The preparation method according to claim 1, characterized in that, The puncture-resistant reinforcing material mentioned in step S2 is selected from one or more of glass fiber, aramid fiber, nano-silica, alumina, or silicon powder.

6. The preparation method according to claim 1, characterized in that, The preparation process of the coating slurry in step S2 includes: first stirring each component at a speed of 80-100 r / min for 20 minutes, and then increasing the speed to 450-550 r / min and stirring for 60 minutes.

7. The preparation method according to claim 1, characterized in that, According to the preparation method of claim 1, the blade gap in the blade coating process in step S3 is 80-85 μm, and the coating speed is 3.5-4.0 m / min.

8. The preparation method according to claim 1, characterized in that, The coating slurry has a thixotropic coefficient of 2.2 to 3.5, a solid content of 40% to 90%, and a shear viscosity of 5000 to 20000 mPa·s.

9. The preparation method according to claim 1, characterized in that, The heat dissipation film has a dry film thickness of 30–1000 μm, an in-plane thermal conductivity of ≥70 W / (m·K), a breakdown voltage of ≥10 kV, and, under the condition of a radius of curvature of 5 mm, a heat dissipation film that can withstand ≥10,000 folds without breaking.

10. A heat dissipation film for a mobile phone battery protection circuit, characterized in that, It is prepared by any one of claims 1 to 9.