Polyamide-based heat-conducting carbon adhesive and preparation method thereof

Abstract

The invention belongs to the technical field of heat-conducting glue materials, and particularly relates to polyamide-based heat-conducting carbon glue and a preparation method thereof. The preparation method comprises the following steps: sequentially adding graphite, binary organic acid and an activating agent into molten caprolactam, uniformly mixing, heating to react for a period of time, continuously adding a chain extender, sodium hydroxide and a graphite intercalation compound, and uniformly stirring to obtain a mixed system; and after the temperature of the mixed system is stable, adding ethanol, and continuously stirring until the temperature of the mixed system is stable again to obtain the polyamide-based heat-conducting carbon adhesive. The polyamide-based heat-conducting carbon adhesive prepared by the invention is excellent in heat conductivity and high in chemical stability, and can be suitable for various use scenes.

Description

Technical Field

[0001] This invention belongs to the field of thermally conductive adhesive materials technology, specifically relating to a polyamide-based thermally conductive carbon adhesive and its preparation method. Background Technology

[0002] With the rapid development of the field of artificial intelligence (AI), the functional circuits of electronic chips in intelligent devices are gradually shifting towards higher integration and higher frequency. In high-density integrated electronic device systems, thermal management during operation is particularly important to reduce the safety hazards caused by localized overheating. For example, third-generation semiconductors and their derivative devices, represented by AI chips and silicon carbide (SiC) power devices, have localized heat flux densities exceeding 500 W / cm² during operation. 2 Traditional thermal interface materials (such as silicone grease and epoxy resin composites) have defects such as low thermal conductivity and insufficient thermal stability, which can lead to uncontrolled junction temperature of devices during long-term use or in high-temperature environments. In severe cases, this can even cause performance degradation or functional failure. Furthermore, the preparation process of traditional thermal interface materials is relatively complex, with high production costs and the generation of toxic waste.

[0003] Against this backdrop, the development of novel thermal interface materials that are simple to prepare, produce environmentally friendly and recyclable products, are inexpensive, have excellent thermal conductivity, and exhibit good operational stability has become a global consensus for promoting sustainable development. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies, the primary objective of this invention is to provide a method for preparing polyamide-based thermally conductive carbon adhesive. This method innovatively combines graphite, graphite intercalation compounds (GICs), and caprolactam monomer in-situ anionic polymerization system. By using toluene diisocyanate as an activator and sodium caprolactam salt as an initiator, the caprolactam anionic polymerization system can rapidly undergo polymerization in a very short time. This tightly links graphite and GICs through PA molecular chains, enhancing lattice vibration phenomena and improving the thermally conductive carrier transport network, thereby preparing a polyamide-based thermally conductive carbon adhesive with excellent performance.

[0005] The second objective of this invention is to provide a polyamide-based thermally conductive carbon adhesive obtained by the above preparation method. This polyamide-based thermally conductive carbon adhesive has an organic molecular chain segment coating-bonded inorganic nanosheet structure, exhibits excellent thermal conductivity and high chemical stability at normal operating temperatures, and is suitable for various application scenarios.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for preparing a polyamide-based thermally conductive carbon adhesive includes the following steps:

[0008] Under stirring conditions, graphite, a dibasic organic acid, and an activator were added sequentially to the melted caprolactam. After heating and reacting for a period of time, a chain extender, sodium hydroxide, and graphite interlayer compound were added to obtain a mixed system. After the temperature of the mixed system stabilized, ethanol was added, and stirring was continued until the temperature of the mixed system stabilized again, thus obtaining the polyamide-based thermally conductive carbon adhesive.

[0009] To avoid excessive chain transfer and cross-linking reaction, this invention uses ethanol for end-capping. Ethanol reacts exothermically with the chain-end functional groups, which can cause system temperature instability. Therefore, the stability of the system after the addition of ethanol is also a standard for the completion of the reaction.

[0010] In this invention, after heating and reacting for a period of time, a chain extender, sodium hydroxide, and graphite intercalation compound are added. The sodium caprolactam salt, formed in situ from some of the caprolactam and sodium hydroxide, can act as an initiator. Compared to the traditional initiator sodium hydride, sodium caprolactam salt as an initiator can reduce the generation of byproducts and, to some extent, improve the conversion rate of caprolactam.

[0011] Furthermore, the graphite interlayer compound is prepared by the following process: multilayer scaly graphite powder, zinc salt, lithium fluoride and hydrochloric acid solution are mixed, heated and stirred, and then sodium hydroxide is added. The mixture is stirred and centrifuged, and the collected product is dispersed in a polar organic solvent for ultrasonic exfoliation. After filtration and drying, the graphite interlayer compound is obtained.

[0012] The present invention uses lithium fluoride as an intercalating agent, which is more conducive to the insertion of lithium ions into the graphite interlayer, weakens the van der Waals forces, and enables the graphite interlayer to expand and peel off.

[0013] This invention introduces graphite intercalation compounds (GICs) into the caprolactam anionic in-situ polymerization system. During the preparation of GICs, lithium ions and sodium ions can disrupt the interlayer structure of multilayer scaly graphite powder, zinc ions stabilize and expand the interlayer structure through complexation, and the polymeric organic solvent acts as an interlayer lubricant, thereby obtaining stable graphite intercalation compounds (GICs). GICs can provide growth sites for CL ring-opening polymerization while enhancing the phonon transport rate and preventing graphite agglomeration.

[0014] Furthermore, the ratio of multilayer scaly graphite powder, zinc salt, lithium fluoride, hydrochloric acid solution, sodium hydroxide and polar organic solvent is 1g:0.2g:0.35g:4mL:0.4g:6mL.

[0015] The proportions used in this invention were derived through multiple experiments and improvements. This proportion is beneficial for the repeated preparation of high-quality thermally conductive carbon adhesive.

[0016] Furthermore, the concentration of the hydrochloric acid solution is 14 mol / L; the polar organic solvent is dimethyl sulfoxide.

[0017] The present invention uses dimethyl sulfoxide, which has a better effect on secondary intercalation and exfoliation and solute dispersion.

[0018] Furthermore, the heating and stirring temperature is 40-60℃, and the time is 20-30 minutes; the stirring time is 20-30 minutes.

[0019] Furthermore, the dibasic organic acid is terephthalic acid; the activator is toluene diisocyanate; and the chain extender is polyethylene glycol.

[0020] This invention uses short-chain bifunctional toluene diisocyanate containing a benzene ring as an activator, which has fast initiation characteristics.

[0021] This invention involves sequentially adding graphite, a dibasic organic acid, and the activator toluene diisocyanate to molten caprolactam. Part of the caprolactam reacts with toluene diisocyanate to generate an active intermediate (chemical structure shown in Formula 1), which can more effectively reduce the reaction energy barrier, accelerate the formation rate of molecular chains, and provide a certain steric hindrance, reducing the probability that the active anion of caprolactam is encapsulated in polyamide (PA) crystals.

[0022]

[0023] Furthermore, the polyethylene glycol is of the type polyethylene glycol (PEG Mn = 800).

[0024] Furthermore, the ratio of caprolactam, graphite, dibasic organic acid, and activator is 1g:0.2g:0.075g:0.5mL.

[0025] The proportions used in this invention were derived through multiple experiments and improvements. This proportion is beneficial for the repeated preparation of high-quality thermally conductive carbon adhesive.

[0026] Furthermore, the mass ratio of caprolactam, chain extender, sodium hydroxide, and graphite intercalation compound is 1:0.15:0.06:0.05.

[0027] The proportions used in this invention were derived through multiple experiments and improvements. This proportion is beneficial for the repeated preparation of high-quality thermally conductive carbon adhesive.

[0028] By adopting the above technical solution, the introduction of graphite interlayer compounds can effectively improve the distribution of graphite sheets, form a more complete thermal conductivity pathway inside the polyamide, provide growth sites for the ring-opening polymerization of caprolactam, enhance the phonon transport rate, avoid graphite aggregation, and the graphite interlayer compounds can work together with graphite to provide growth sites for the growth of polyamide molecular chains. During the growth process, the polyamide molecules will also connect the graphite and the graphite interlayer compounds to each other, forming a stable thermal conductivity pathway with flat orientation under the action of terephthalic acid.

[0029] Furthermore, the heating reaction is carried out at a temperature of 110-120°C for 10-20 minutes.

[0030] A polyamide-based thermally conductive carbon adhesive is prepared by the above-described method for preparing polyamide-based thermally conductive carbon adhesive.

[0031] The beneficial technical effects of this invention are as follows:

[0032] (1) This invention is the first to combine graphite, graphite intercalation compounds (GICs) with an in-situ anionic polymerization system of caprolactam monomer. By using toluene diisocyanate as an activator and sodium caprolactam salt as an initiator, active sites are constructed on the surface of graphite sheets to promote the ring-opening of caprolactam to form polyamide (PA), thereby achieving precise control of the polymerization reaction rate and effectively reducing the generation of microphase separation. At the same time, the introduction of graphite intercalation compounds (GICs) can effectively improve the distribution of graphite sheets and form a more complete thermal conductivity pathway inside PA, thereby enhancing the thermal conductivity of the composite material. In addition, the introduced dibasic organic acid (terephthalic acid) and polyethylene glycol can regulate the overall flowability of the composite material while ensuring the directional arrangement of graphite sheets in the viscous matrix (Herman orientation factor > 0.85).

[0033] (2) The present invention is based on the preparation method of caprolactam anionic ring-opening polymerization with fast reaction rate (reaction time < 15 min) and high conversion rate (conversion efficiency 99.9%). It does not require pretreatment of thermally conductive fillers, solvent removal or post-curing process, which can effectively reduce production energy consumption.

[0034] (3) The polyamide-based thermally conductive carbon adhesive prepared by the present invention has excellent thermal conductivity, which is attributed to the synergistic effect between internal thermally conductive materials. The interaction between graphite sheets and GICs constructs a complete and reliable thermally conductive network inside the PA. At the same time, the two-dimensional sheet material can effectively improve the phonon transmission efficiency and enhance the vibration wave of the lattice vibration inside the PA, thereby improving the thermal conductivity. Attached Figure Description

[0035] Figure 1 A schematic diagram of the structure of the graphite interlayer compound used in the preparation example;

[0036] Figure 2 This is a flowchart illustrating the preparation process of the polyamide-based thermally conductive carbon adhesive of Example 1 of the present invention.

[0037] Figure 3 This describes the bonding method between caprolactam and anionic polymerized polyamide on the surface of graphite and graphite intercalation compounds (GICs) during the preparation process of Example 1 of the present invention.

[0038] Figure 4 These are photographs of the products obtained in Example 1 and Comparative Examples 1-5 of the present invention after being left to stand at room temperature for 24 hours.

[0039] Figure 5 These are photographs of the products obtained in Example 1 and Comparative Examples 1-5 of the present invention after being soaked in deionized water at room temperature for 24 hours.

[0040] Figure 6 The following are DSC data graphs of the products obtained in Example 1 and Comparative Example 3 of this invention in the range of 20℃-350℃;

[0041] Figure 7 This is a graph showing the heat conduction data of the product obtained in Example 1 of the present invention within 6 minutes;

[0042] Figure 8 The diagram shows the heat conduction effect of the product obtained in Example 1 of the present invention at different temperatures. Detailed Implementation

[0043] The following is a further detailed description of the present invention in conjunction with specific preferred embodiments, and it should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention. Specific conditions not specified in the embodiments are performed according to conventional conditions or conditions recommended by the manufacturer. Unless otherwise specified, all reagents or instruments used are conventional products obtained through commercial channels.

[0044] (I) Preparation Example

[0045] 10g of multilayer scaly graphite powder, 2g of zinc acetate (COO-Zn), 3.5g of lithium fluoride (LiF), and 40mL of hydrochloric acid solution (HCl 14mol / L) were mixed in a beaker to form a mixed solution. The mixed solution was then heated to 40℃ in a water bath at 1200rpm for 30min. After stirring, 4g of sodium hydroxide was added to the mixed solution, and heating and stirring continued for another 30min to obtain a precursor solution. The precursor solution was centrifuged at 8000rpm for 5min, and the centrifuged product was dispersed in 60mL of dimethyl sulfoxide (DMSO) and ultrasonically exfoliated for 30min. The mixture was then vacuum filtered, and the solid was removed and dried in a forced-air drying oven at 110℃ for 4h to obtain graphite intercalation compounds (GICs). A schematic diagram of the structure of this graphite intercalation compound is shown below. Figure 1 As shown.

[0046] (II) Implementation Examples

[0047] Example 1

[0048] Example 1 provides a method for preparing a polyamide-based thermally conductive carbon adhesive. The specific preparation method is as follows:

[0049] Add 20g of caprolactam to a 500mL single-necked flask and heat to 85℃ to completely melt the caprolactam. While stirring at 1200rpm, add 4g of graphite particles, 1.5g of terephthalic acid, and 10mL of toluene diisocyanate (TDI) to the flask and mix thoroughly. Heat to 120℃ and react for 10min. Then, add 3g of polyethylene glycol (PEG Mn=800), 1.2g of sodium hydroxide, and 1g of graphite intercalation compounds (GICs) in sequence, and continue stirring until the mixture is homogeneous to obtain a mixed system. When the temperature of the mixed system remains constant or decreases slightly, add 6mL of anhydrous ethanol. Wait for the reaction temperature to remain constant or be maintained at 120℃, then stop stirring and heating. Pour the reaction system out of the flask to obtain polyamide-based thermally conductive carbon adhesive.

[0050] The above preparation process flowchart is as follows: Figure 2 As shown, the bonding mechanism between caprolactam and anionic polyamide on the surfaces of graphite and graphite intercalation compounds (GICs) during the preparation process is as follows: Figure 3 As shown.

[0051] Example 1 also provides a polyamide-based thermally conductive carbon adhesive, which is prepared by the above preparation method.

[0052] (III) Comparative Example

[0053] Comparative Example 1

[0054] Comparative Example 1 is basically the same as Example 1, except that the graphite intercalation compound (GICs) in Example 1 is omitted, while the amounts of other substances remain unchanged.

[0055] Comparative Example 2

[0056] Comparative Example 2 is basically the same as Example 1, except that the graphite intercalation compounds (GICs) in Example 1 are replaced with an equal amount of graphite particles.

[0057] Comparative Example 3

[0058] Comparative Example 3 is basically the same as Example 1, except that 1g of graphite intercalation compound (GICs) in Example 1 is replaced with 0.5g of carbon nanotubes and 0.5g of graphite intercalation compound (GICs).

[0059] Comparative Example 4

[0060] Comparative Example 4 is basically the same as Example 1, except that the amount of graphite particles used in Example 1 is adjusted to 3g and the amount of graphite intercalation compound (GICs) is adjusted to 2g.

[0061] Comparative Example 5

[0062] Comparative Example 5 is basically the same as Example 1, except that the amount of graphite particles used in Example 1 is adjusted to 2g and the amount of graphite intercalation compound (GICs) is adjusted to 3g.

[0063] (iv) Test Examples

[0064] Embodiment 1 of the present invention is named Group A, and Comparative Examples 1-5 are named Groups B, C, D, E and F.

[0065] The actual images of the products prepared in Example 1 and Comparative Examples 1-5 after standing for 24 hours are shown below. Figure 4 As shown in the figure, after the materials were left to stand for 24 hours in a natural atmosphere without inert gas protection at room temperature and pressure, the apparent physical state of the samples in group A (Example 1) and group D (Comparative Example 3) did not change significantly and remained in a viscous flow state. This is because, under these conditions, the polyamide-based thermally conductive carbon adhesive did not experience an "island effect" due to excessive material aggregation, and the polyamide molecular chains could effectively connect most of the thermally conductive reinforced carbon-based materials. The results indicate that group A (Example 1) and group D (Comparative Example 3) have excellent component stability under normal conditions and can effectively adhere to the surface of the thermally conductive medium.

[0066] The actual images of the products prepared in Example 1 and Comparative Examples 1-5 after soaking in deionized water for 24 hours are shown below. Figure 5As shown in the figure, after the materials were left to stand in a water-immersed atmosphere without inert gas protection at room temperature and pressure for 24 hours, the apparent properties of Group A (Example 1), with a graphite to graphite intercalation compound (GICs) mass ratio of 4:1, and Group D (Comparative Example 3), with a graphite to carbon nanotube and graphite intercalation compound (GICs) mass ratio of 4:0.5:0.5, did not change significantly and remained in a viscous flow state, while the samples of other components all showed swelling. This is because, as described in result (1), the carbon-based thermally conductive reinforcing material has a better distribution orientation inside the polyamide (PA) matrix. The dense and continuously distributed carbon material and the hydrogen bonds formed between it and terephthalic acid form a "barrier" around the polyamide (PA) molecular chain. This phenomenon can effectively prevent water molecules from invading into the material, which will greatly increase the resistance of the polyamide (PA) molecular chain to water molecules. The results show that the samples in group A (Example 1) and group D (Comparative Example 3) have excellent component stability in the immersion environment, which can greatly extend the service life of polyamide-based thermally conductive carbon adhesive in humid or immersion environments.

[0067] This invention selected Group A (Example 1) and Group D (Comparative Example 3), which exhibited superior environmental stability, and conducted DSC tests with programmed temperature rise and fall within a temperature range of 20℃-350℃. The DSC data are as follows: Figure 6 As shown, (a) corresponds to group A, and (b) corresponds to group D. From Figure 6 As can be seen in (a), the cold crystallization temperature of the samples in group A (Example 1) is around 30℃, and the melting temperature is around 345℃. Furthermore, the heat flow curves during continuous heating and cooling are relatively stable, indicating that the theoretical operating limit of this group of samples is between 30℃ and 345℃. This is because the heat-conducting charge carriers inside the material are mainly phonons. Phonons are generated and transported through lattice vibrations between crystals within the polymer matrix. Therefore, crystalline thermally conductive carbon adhesives have a wider phonon transport path than amorphous thermally conductive carbon adhesives, and their thermal conductivity is much higher. Similarly, it can be proven from... Figure 6 As can be seen in (b), the theoretical operating temperature range of sample D (Comparative Example 3) is between 24℃ and 256℃. Compared with sample A (Example 1), the theoretical operating temperature range of sample D (Comparative Example 3) is smaller, which has certain limitations in the application of thermal conductive materials. This is because carbon nanotubes are carbon materials with a 3D honeycomb tubular structure. During the crystallization process, polymer materials will experience a certain "thermal shrinkage" phenomenon due to the movement of molecular chains. Carbon nanotubes will expose the polyamide (PA) molecular chains to the air during the heating process, causing oxidation and decomposition. Therefore, the theoretical maximum operating temperature of sample D (Comparative Example 3) is lower than that of sample A (Example 1).

[0068] This invention selects Group A (Example 1), which has superior overall performance, for actual thermal conductivity testing. The data are as follows: Figure 7 , Figure 8 As shown. Figure 7 In this context, "Set Temperature" refers to the hot stage temperature, and "Material Testing Temperature" refers to the temperature of the polyamide-based thermally conductive carbon adhesive material prepared in Example 1 after it has been placed on the hot stage for different times. Figure 8 It can be seen that the sample in Group A (Example 1) of this invention has excellent thermal conductivity and efficiency, and can quickly bring its own temperature to match the temperature of the hot plate, demonstrating rapid thermal response. From Figure 8 As can be seen from (a)-(f), the sample of Group A (Example 1) of the present invention has reliable thermal conductivity. It can still maintain good thermal conductivity during temperature gradient changes within a small range (102℃-103℃-105℃) and has reliable thermal conductivity sensitivity.

[0069] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. The basic principles and main features of the present invention have been described above with specific implementation schemes. Based on the present invention, some modifications or substitutions can be made, but these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of protection claimed by the present invention.

Claims

1. A method for preparing a polyamide-based thermally conductive carbon adhesive, characterized in that, Includes the following steps: Graphite, dibasic organic acid, and activator are added sequentially to melted caprolactam and mixed evenly. After heating and reacting for a period of time, chain extender, sodium hydroxide, and graphite interlayer compound are added and stirred evenly to obtain a mixed system. After the temperature of the mixed system stabilizes, ethanol is added and stirred continuously until the temperature of the mixed system stabilizes again, thus obtaining the polyamide-based thermally conductive carbon adhesive.

2. The method for preparing polyamide-based thermally conductive carbon adhesive according to claim 1, characterized in that, The graphite interlayer compound is prepared by the following process: multilayer scaly graphite powder, zinc salt, lithium fluoride and hydrochloric acid solution are mixed, heated and stirred, and then sodium hydroxide is added. The mixture is stirred and centrifuged, and the collected product is dispersed in a polar organic solvent for ultrasonic exfoliation. After filtration and drying, the graphite interlayer compound is obtained.

3. The method for preparing polyamide-based thermally conductive carbon adhesive according to claim 2, characterized in that, The ratio of the multilayer scaly graphite powder, zinc salt, lithium fluoride, hydrochloric acid solution, sodium hydroxide and polar organic solvent is 1g:0.2g:0.35g:4mL:0.4g:6mL.

4. The method for preparing polyamide-based thermally conductive carbon adhesive according to claim 2, characterized in that, The concentration of the hydrochloric acid solution is 14 mol / L; the polar organic solvent is dimethyl sulfoxide.

5. The method for preparing polyamide-based thermally conductive carbon adhesive according to claim 2, characterized in that, The heating and stirring temperature is 40-60℃, and the time is 20-30 minutes; the stirring time is continued for 20-30 minutes.

6. The method for preparing polyamide-based thermally conductive carbon adhesive according to claim 1, characterized in that, The dibasic organic acid is terephthalic acid; the activator is toluene diisocyanate; and the chain extender is polyethylene glycol.

7. The method for preparing polyamide-based thermally conductive carbon adhesive according to claim 1, characterized in that, The ratio of caprolactam, graphite, dibasic organic acid and activator is 1g:0.2g:0.075g:0.5mL.

8. The method for preparing polyamide-based thermally conductive carbon adhesive according to claim 1, characterized in that, The mass ratio of caprolactam, chain extender, sodium hydroxide, and graphite intercalation compound is 1:0.15:0.06:0.

05.

9. The method for preparing polyamide-based thermally conductive carbon adhesive according to claim 1, characterized in that, The heating reaction is carried out at a temperature of 110-120℃ for 10-20 minutes.

10. A polyamide-based thermally conductive carbon adhesive, characterized in that, It is prepared by the method described in any one of claims 1-8 for preparing polyamide-based thermally conductive carbon adhesive.

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