A PTFE composite material with high thermal conductivity and low dielectric loss and its preparation method

Abstract

The present invention relates to the technical field of composite material preparation, and particularly relates to a PTFE composite material with high thermal conductivity and low dielectric loss and a preparation method thereof. The PTFE composite material comprises the following components: PTFE resin, hexagonal boron nitride, other fillers, surfactant and thickener, wherein the PTFE resin is prepared by mixing PTFE emulsion and PTFE micro powder. The preparation method of the present invention is simple, the material has excellent thermal conductivity and low dielectric loss, meets the application requirements of high-performance copper clad laminates, and solves the problems of poor thermal conductivity of existing PTFE composite materials and the inability to take into account low dielectric loss.

Description

Technical Field

[0001] The present invention relates to the technical field of composite material preparation, and particularly relates to a PTFE composite material with high thermal conductivity and low dielectric loss and a preparation method thereof. Background Art

[0002] High-performance copper clad laminates are key basic materials urgently needed in fields such as autonomous driving millimeter-wave radars, high-precision satellite navigation, 5G base stations, military, and national defense. In recent years, with the rapid development of microelectronics information technology, electronic products are increasingly developing towards miniaturization and high frequency, which has brought a greater impact on traditional copper clad laminates and put forward higher requirements for the thermal conductivity, dielectric properties, and bonding properties of copper clad laminates to ensure the normal operation of electronic devices and the integrity of signal transmission. Currently, the polymers applied to high-frequency copper clad laminates include: modified epoxy resin, polytetrafluoroethylene resin (PTFE), high-density polyethylene (HDPR), polypropylene, polyimide resin, etc. Among them, PTFE, as a high-performance matrix resin with the lowest theoretical value of dielectric loss (0.0001), is the recognized main and most commercialized material approach. However, due to its inherent defects such as poor processing performance, insufficient thermal conductivity, and poor bonding performance, its application in the copper clad laminate industry has been restricted.

[0003] To solve the problem of poor thermal conductivity of PTFE, mainly organic / inorganic fillers such as ceramics and glass fibers are used to fill PTFE to prepare composite materials, and certain results have been achieved. However, the improvement of the thermal conductivity of PTFE composite materials is limited.

[0004] Chinese invention patent CN115534441A discloses a PTFE copper clad laminate with high thermal conductivity and heat resistance and a manufacturing method thereof. By subjecting a glass fiber cloth to high-temperature sintering, washing it after sintering, and then drying its moisture to ensure the cleanliness of the proportion fiber cloth, impregnating the pretreated glass fiber cloth in a mixed slurry of PTFE / FEP / silicon carbide / coupling agent, taking it out and drying it, and then loading a copper foil, a PTFE composite material with a dielectric loss of 0.0011 and a thermal conductivity of 0.55 W / mK is obtained. Chinese invention patent CN109181178B discloses a preparation method of a high-thermal-conductivity polytetrafluoroethylene composite membrane material, which is mainly prepared by methods such as filler modification, high-speed mixing, cold pressing into a blank, sintering molding, turning into a film, and calendering orientation, and a BN-BNNTs / PTFE composite material with a dielectric loss of 0.0066 and a thermal conductivity of 1.23 W / mK is prepared. Although the method has played a certain role in improving the low thermal conductivity of PTFE, it is not significant. At the same time, the selection of raw materials and the preparation method often lead to a significant increase in dielectric loss. Therefore, the key to the present invention is how to improve the thermal conductivity of PTFE while ensuring low dielectric loss and high bonding strength. Summary of the Invention

[0005] Aiming at the above-mentioned defects, the purpose of the present invention is to provide a PTFE composite material with high thermal conductivity and low dielectric loss and a preparation method thereof. The preparation method of the present invention is simple, the material has excellent thermal conductivity, low dielectric loss and strong bonding performance, meets the application requirements of high-performance copper clad laminates, and solves the problems of poor thermal conductivity of existing PTFE composite materials and the inability to balance low dielectric loss and good bonding performance.

[0006] In order to achieve the above purpose, the present invention adopts the following technical solutions:

[0007] The present invention provides a PTFE composite material with high thermal conductivity and low dielectric loss. The PTFE composite material comprises the following components: PTFE resin, hexagonal boron nitride, other fillers, surfactant and thickener. The PTFE resin is prepared by mixing PTFE emulsion and PTFE micropowder. By adding PTFE micropowder, the distribution of fillers is improved, and the thermal conductivity can be effectively improved while ensuring low dielectric and high bonding strength.

[0008] Further, the solid content of the PTFE emulsion is 45-60 wt%, and the D50 is 0.20-1 μm.

[0009] Further, the D50 of the PTFE micropowder is 2-20 μm.

[0010] Further, the ratio of the PTFE emulsion to the PTFE micropowder is a solid volume ratio of 1-6:1. As used herein, the solid volume ratio means the volume ratio of the PTFE solid phase contained in the PTFE emulsion to the PTFE micropowder.

[0011] Further, the other fillers include one or more of silicon nitride, silicon carbide, alumina, cubic boron nitride, silica or titanium dioxide.

[0012] Further, the surfactant is a silane coupling agent, a borate coupling agent, a phosphate coupling agent, a titanate coupling agent, preferably a silane coupling agent.

[0013] Further, the thickener is one or two of polyoxyethylene-based styrylated phenyl ether, carboxymethyl cellulose, polyvinyl alcohol or gelatin, preferably polyoxyethylene-based styrylated phenyl ether.

[0014] Further, the volume ratio of the hexagonal boron nitride, other fillers, surfactant, thickener to the PTFE resin is 0-50:0-40:0-1:0-1:40-90.

[0015] It should be understood that as described herein, the PTFE resin refers to the PTFE solid, which is the general term for the PTFE solids in the raw materials for preparing the PTFE resin (i.e., PTFE emulsion and PTFE micropowder). That is to say, the volume fraction of the PTFE resin mentioned in this article refers to the volume fraction occupied by the PTFE solid, which is the total volume of the PTFE solids in the raw materials for preparing the PTFE resin (i.e., PTFE emulsion and PTFE micropowder).

[0016] Furthermore, the thermal conductivity of the PTFE composite material is greater than 1.5 W / m K, preferably greater than 1.7 W / m K, and can reach 1.528 - 2.06 W / m K for example. The dielectric loss under the condition of 10 GHz is less than 0.0005, and the bonding strength is greater than 0.8 N / mm.

[0017] The present invention also provides a method for preparing a PTFE composite material with high thermal conductivity and low dielectric loss as described herein, which includes the following steps:

[0018] (1) Preparation of the PTFE resin mixed emulsion: Mix the PTFE emulsion and the PTFE micropowder, and add deionized water to make the solid content of the PTFE resin mixed emulsion 45 - 60 wt%.

[0019] (2) Mixing of raw materials: Mix hexagonal boron nitride, other fillers, surfactant, thickener with the PTFE resin mixed emulsion and defoam to obtain the PTFE mixed compound.

[0020] (3) Coating, sintering and forming: Form a film from the PTFE mixed compound, then dry, sinter and cool to obtain the PTFE composite film.

[0021] (4) Secondary pressing: Hot press the PTFE composite film to obtain the PTFE composite material.

[0022] Furthermore, the film formation in step (3) is carried out on a PI film, dried at 50 - 80 °C until the moisture is completely volatilized, and sintered at 360 - 380 °C for 10 - 15 min.

[0023] Furthermore, step (4) is hot pressing at 350 - 380 °C under a pressure of 300 - 500 psi for 1 - 2 h.

[0024] Furthermore, in the PTFE composite material obtained by the above method, the volume ratio of hexagonal boron nitride, other fillers, surfactant, thickener to the PTFE resin is 0 - 50:0 - 40:0 - 1:0 - 1:40 - 90.

[0025] Advantages of the present invention:

[0026] 1. The PTFE composite material obtained by the present invention has excellent high-frequency dielectric properties and thermal conductivity. Its dielectric loss (10 GHz) is less than 0.0005, the bonding strength is greater than 0.8 N / mm, and the thermal conductivity can reach 2.06 W / m K. The performance is significantly higher than the industry level and can be used in fields such as high-frequency and high-speed circuits.

[0027] 2. The present invention selects boron nitride as the main filler. The intrinsic high thermal conductivity and low dielectric loss properties of boron nitride have a positive effect on improving the thermal conductivity of the PTFE composite material and controlling the dielectric loss and bonding strength.

[0028] 3. The present invention selects the compound of PTFE emulsion and PTFE micropowder as the polymer matrix. During the film-forming process, the presence of PTFE micropowder restricts the horizontal orientation of flaky boron nitride and increases the content of boron nitride in the vertical direction of the PTFE film, effectively improving its thermal conductivity.

[0029] 4. The present invention selects PTFE micropowder to limit the distribution of boron nitride in the polymer matrix, making boron nitride more inclined to connect with each other to form a thermal conduction network structure, thereby effectively improving the thermal conductivity and enabling the PTFE composite material to meet the application requirements.

[0030] 5. The PTFE composite material prepared by the present invention can adjust the sample thickness and internal structure by changing the coating process, or can be formed by hot pressing and melting multiple layers of materials later. It has high operability and process performance, and the prepared PTFE composite material has excellent uniformity. Description of the Drawings

[0031] Figure 1 is the cross-sectional morphology of the PTFE composite material obtained in Example 4. Detailed Embodiments

[0032] The following specific embodiments are used to further illustrate the present invention, but the embodiments do not limit the present invention in any form. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in the technical field.

[0033] In the examples and comparative examples of the present invention, the PTFE raw materials used are PTFE emulsion with a solid content of 60 wt% and D50 of 0.21 - 0.25 μm, and PTFE micropowder with D50 of 2 - 5 μm. The solid volume ratio of the PTFE emulsion and micropowder used is 3:1, 1:1, 1:3.

[0034] In the examples and comparative examples, the PTFE emulsion is purchased from Shandong Dongyue Polymer Materials Co., Ltd., the PTFE emulsion grade is DF-331Z, and the PTFE micropowder grade is DF-521T.

[0035] Example 1

[0036] A PTFE composite material, comprising the following components by volume percentage: 35% hexagonal boron nitride, 10% silicon dioxide, 10% titanium dioxide, 45% PTFE resin, and its preparation method is as follows:

[0037] (1) According to the required amount of PTFE resin, mix PTFE emulsion and PTFE micropowder with a solid volume ratio of 1:1, and add deionized water to ensure that the solid content of the PTFE resin mixed emulsion is 60% to obtain the PTFE resin mixed emulsion. Then mix the required amounts of hexagonal boron nitride, silicon dioxide, titanium dioxide, and PTFE resin mixed emulsion evenly, add an appropriate amount of polyoxyethylene-based styrylated phenyl ether, stir at high speed for 20 min to mix evenly, and defoam to obtain the PTFE mixed rubber compound;

[0038] (2) Coat the PTFE mixed rubber compound obtained in step (1) on a PI film, control the coating thickness to be 250 μm, dry the coated PI film in an oven at 60 °C for 15 min until the moisture is completely volatilized, and sinter it in an oven at 365 °C for 15 min until it is formed;

[0039] (3) After overlapping 2 pieces of the PTFE composite film prepared in step (2), perform hot pressing at a temperature of 370 °C and a pressure of 400 psi for 1 h. After cooling, peel the PTFE composite material from the PI film to obtain a PTFE composite material with uniform thickness and good appearance.

[0040] Example 2

[0041] A PTFE composite material, comprising the following components by volume percentage: 40% hexagonal boron nitride, 7.5% silicon dioxide, 7.5% titanium dioxide, 45% PTFE resin, and its preparation method is as follows:

[0042] (1) According to the required amount of PTFE resin, mix PTFE emulsion and PTFE micropowder with a solid volume ratio of 1:1, and add deionized water to ensure that the solid content of the PTFE resin mixed emulsion is 60% to obtain the PTFE resin mixed emulsion. Then mix the required amounts of hexagonal boron nitride, silicon dioxide, titanium dioxide, and PTFE resin mixed emulsion evenly, add an appropriate amount of polyoxyethylene-based styrylated phenyl ether, stir at high speed for 20 min to mix evenly, and defoam to obtain the PTFE mixed rubber compound;

[0043] (2) Coat the PTFE mixed rubber compound obtained in step (1) on a PI film, control the coating thickness to be 250 μm, dry the coated PI film in an oven at 60 °C for 15 min until the moisture is completely volatilized, and sinter it in an oven at 365 °C for 15 min until it is formed;

[0044] (3) After overlapping two PTFE composite films prepared in step (2), hot press them at a temperature of 370 °C under a pressure of 400 psi for 1 h. After cooling, peel the PTFE composite material from the PI film to obtain a PTFE composite material with uniform thickness and good appearance.

[0045] Example 3

[0046] A PTFE composite material, comprising the following components by volume percentage: 45% hexagonal boron nitride, 5% silicon dioxide, 5% titanium dioxide, 45% PTFE resin. Its preparation method is as follows:

[0047] (1) According to the required amount of PTFE resin, mix PTFE emulsion and PTFE micropowder with a solid volume ratio of 1:1, and add deionized water to ensure that the solid content of the PTFE resin mixed emulsion is 60% to obtain a PTFE resin mixed emulsion. Then, mix the required amounts of hexagonal boron nitride, silicon dioxide, titanium dioxide, and PTFE resin mixed emulsion evenly in deionized water, add an appropriate amount of polyoxyethylene-based biphenylylstyrenated phenyl ether, stir at high speed for 20 min to mix evenly, and defoam to obtain a PTFE mixed rubber compound;

[0048] (2) Coat the PTFE mixed rubber compound obtained in step (1) on a PI film, control the coating thickness to be 200 μm, dry the coated PI film in an oven at 60 °C for 15 min until the moisture is completely volatilized, and sinter it in an oven at 365 °C for 15 min until it is formed;

[0049] (3) After overlapping two PTFE composite films prepared in step (2), hot press them at a temperature of 370 °C under a pressure of 400 psi for 1 h. After cooling, peel the PTFE composite material from the PI film to obtain a PTFE composite material with uniform thickness and good appearance.

[0050] Example 4

[0051] A PTFE composite material, comprising the following components by volume percentage: 50% hexagonal boron nitride, 2.5% silicon dioxide, 2.5% titanium dioxide, 45% PTFE resin. Its preparation method is as follows:

[0052] (1) According to the required amount of PTFE resin, mix PTFE emulsion and PTFE micro-powder with a solid volume ratio of 1:1, and add deionized water to ensure that the solid content of the PTFE resin mixed emulsion is 60% to obtain the PTFE resin mixed emulsion. Then, mix the required amounts of hexagonal boron nitride, silicon dioxide, titanium dioxide, and the PTFE resin mixed emulsion evenly in deionized water, add an appropriate amount of polyoxyethylene-based biphenylstyrenated phenyl ether, stir at high speed for 20 min to mix evenly, and defoam to obtain the PTFE mixed compound;

[0053] (2) Coat the PTFE mixed compound obtained in step (1) on the PI film, control the coating thickness to be 200 μm, dry the coated PI film in an oven at 60 °C for 15 min until the moisture completely evaporates, and sinter it in an oven at 365 °C for 15 min until it is formed;

[0054] (3) After overlapping 2 pieces of the PTFE composite films prepared in step (2), perform hot pressing at a temperature of 370 °C and a pressure of 400 psi for 1 h. After cooling, peel the PTFE composite material from the PI film to obtain a PTFE composite material with uniform thickness and good appearance.

[0055] Comparative Examples 1-4

[0056] For intuitive comparison, in each of the PTFE composite materials provided in Comparative Examples 1-4, the types and contents of the components are respectively the same as those in Examples 1-4 (for example, Comparative Example 1 is the same as Example 1), and only the PTFE resin is different. The PTFE resin raw materials in Comparative Examples 1-4 only contain PTFE emulsion.

[0057] The preparation methods of the PTFE composite materials in Comparative Examples 1-4 are consistent with the corresponding Examples 1-4.

[0058] Comparative Example 5

[0059] In the PTFE composite material provided in Comparative Example 5, the types and contents of the components are the same as those in Example 4, and only the PTFE resin is different. The PTFE resin in Comparative Example 5 is prepared by mixing PTFE emulsion and PTFE micro-powder with a solid volume ratio of 3:1.

[0060] The preparation method of the PTFE composite material in Comparative Example 5 is consistent with the corresponding Example 4.

[0061] Comparative Example 6

[0062] In a PTFE composite material provided in Comparative Example 6, the types and contents of each component are the same as those in Example 4, except that the PTFE resin is different. In Comparative Example 6, the PTFE resin is prepared by mixing a PTFE emulsion and PTFE micropowder with a solid volume ratio of 1:3.

[0063] The preparation method of the PTFE composite material in Comparative Example 6 is consistent with the corresponding Example 4.

[0064] Performance tests were carried out on the PTFE composite materials provided in Examples 1-4 and Comparative Examples 1-6, including thermal conductivity, dielectric properties and peel strength. The test results are shown in Table 1 below:

[0065] Table 1

[0066] Sample Thermal conductivity (W / mK) Dielectric loss Peel strength (N / mm) Example 1 1.75 0.00043 1.270 Example 2 1.89 0.00048 1.155 Example 3 2.02 0.00040 0.972 Example 4 2.06 0.00042 0.813 Comparative Example 1 1.28 0.00047 1.262 Comparative Example 2 1.41 0.00045 1.145 Comparative Example 3 1.46 0.00039 1.007 Comparative Example 4 1.52 0.00043 0.835 Comparative Example 5 1.528 0.00046 0.985 Comparative Example 6 1.334 0.00048 0.946

[0067] According to the performance data provided in Table 1, in the PTFE composite material provided by the present invention, by using a filler with low dielectric loss (boron nitride), it is ensured that the PTFE composite material has a low dielectric loss; by changing the components of the PTFE matrix resin (introducing large-sized PTFE micropowder), the orientation structure of the flaky filler boron nitride is regulated, thereby improving the thermal conductivity of the PTFE composite material. A parallel comparison of Examples 1-4 and Comparative Examples 1-4 shows that when the dosage is the same, the addition of PTFE micropowder can increase the thermal conductivity by 0.4-0.6 W / m K; as the content of boron nitride increases, the improvement effect on the thermal conductivity is more obvious. This is understood as that a more perfect thermal conduction network structure is formed by high-content boron nitride under the constraint of PTFE micropowder, so that the thermal conductivity of the copper clad laminate can reach 2.06 W / m K. In addition, as the in-plane component of boron nitride increases, the content of boron nitride lying flat on the surface of the PTFE composite material decreases, increasing the contact area between the resin and the copper foil, and to a certain extent improving its peel strength. In Comparative Example 5, the proportion of PTFE micropowder in the PTFE matrix was reduced (the solid volume ratio of PTFE emulsion to PTFE micropowder was 3:1), and it can be seen that the improvement effect on heat conduction is limited. In Comparative Example 6, the proportion of PTFE micropowder in the PTFE matrix was increased (the solid volume ratio of PTFE emulsion to PTFE micropowder was 1:3), but its thermal conductivity decreased instead. The reason is that the increase in the content of PTFE micropowder leads to the introduction of more pores, bringing a greater interfacial thermal resistance and affecting the heat transfer. It can be seen that the formula and structure design of the present invention are reasonable and feasible.

[0068] It should be noted that the description of the present invention provides preferred embodiments of the present invention. However, the present invention can be implemented in many different forms and is not limited to the embodiments described in this specification. These embodiments do not serve as additional limitations to the content of the present invention. The purpose of providing these embodiments is to make the understanding of the disclosed content of the present invention more thorough and comprehensive. Moreover, the above technical features continue to be combined with each other to form various embodiments not listed above, which are all regarded as within the scope described in the description of the present invention. Further, for those of ordinary skill in the art, improvements or modifications can be made based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims of the present invention.

Claims

1. A PTFE composite material with high thermal conductivity and low dielectric loss, characterized in that: The PTFE composite material comprises the following components: PTFE resin, hexagonal boron nitride, other fillers, surfactants and thickeners, wherein the other fillers include one or more of silicon nitride, silicon carbide, aluminum oxide, cubic boron nitride, silicon dioxide or titanium dioxide; The PTFE resin is prepared by mixing PTFE emulsion and PTFE micropowder, wherein the solid volume ratio of PTFE emulsion and PTFE micropowder is 1:

1. The volume ratio of the hexagonal boron nitride, other fillers, surfactants, thickeners and PTFE resin is 0-50: 0-40: 0-1: 0-1: 40-90; In addition, the solid content of the PTFE emulsion is 45-60wt%, and the D50 is 0.20-1 μm; the D50 of the PTFE micropowder is 2-20 μm.

2. The PTFE composite material according to claim 1, characterized in that The surfactant is a silane coupling agent, a borate coupling agent, a phosphate coupling agent, or a titanate coupling agent.

3. The PTFE composite material according to claim 1, characterized in that The thickener is one or two of polyoxyethylene distyrenated phenyl ether, carboxymethyl cellulose, polyvinyl alcohol or gelatin.

4. The PTFE composite material according to claim 1, characterized in that The PTFE composite material has a thermal conductivity greater than 1.7 W / m K, a dielectric loss less than 0.0005 under a 10 GHz condition, and a bonding strength greater than 0.8 N / mm.

5. A method for preparing a PTFE composite material with high thermal conductivity and low dielectric loss according to any one of claims 1 to 4, characterized in that: The following steps are involved: (1) Preparation of PTFE resin mixed emulsion: PTFE emulsion and PTFE micropowder are mixed, and deionized water is added to make the solid content of the PTFE resin mixed emulsion be 45-60wt%; (2) Raw material mixing: mixing hexagonal boron nitride, other fillers, surfactants, thickeners and PTFE resin mixed emulsion and degassing to obtain PTFE mixed rubber; (3) Coating and sintering: The PTFE mixed rubber material is formed into a film, and then dried, sintered and cooled to obtain a PTFE composite film; (4) Secondary pressing: The PTFE composite film is hot-pressed to obtain a PTFE composite material.

6. The preparation method according to claim 5, characterized in that: The film formation in step (3) is carried out on the PI film, dried at 50-80°C until the water is completely volatilized, and sintered at 360-380°C for 10-15 min.

7. The preparation method according to claim 5, characterized in that: The step (4) is hot pressing at 350-380°C and a pressure of 300-500 psi for 1-2 h.

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