Application of LDH / polymer in preparation of electromagnetic shielding film

Abstract

The present invention belongs to the technical field of electromagnetic shielding material preparation, and specifically relates to an application of LDH / polymer in the preparation of electromagnetic shielding membranes; the present invention prepares an LDH / polymer solution through a co-precipitation method, thereby improving the binding property of the polymer and LDH and avoiding the problem of LDH peeling off in the polymer matrix; then a certain water-soluble solvent is added to the LDH / polymer mixed solution to cause part of the polymer to precipitate and deposit on the surface of the LDH layer, and the LDH / polymer settles in the solution. Since the polymer chains are entangled with each other, the LDH / polymer has ductility and film-forming characteristics; finally, a surface coating method is used to solve the problem that inorganic nanoparticle materials cannot form films independently, and an LDH / polymer electromagnetic shielding membrane is prepared using film-forming technology; and by controlling the amount and time of solvent addition and adjusting the ratio of LDH / polymer, LDH membranes with different electromagnetic shielding properties are prepared, and the preparation process is simple, environmentally friendly, has few by-products, and can reduce industrialization costs.

Description

Technical Field

[0001] The invention belongs to the technical field of electromagnetic shielding material preparation, and particularly relates to an application of LDH / polymer in the preparation of electromagnetic shielding films. Background Art

[0002] With the advent of the high-frequency, high-speed 5G era, the number of connected devices and antennas has increased exponentially. While electronic technology has brought immense convenience to people's lives, it has also exposed them to constant electromagnetic radiation pollution. Electromagnetic waves generated by various electronic devices can cause electromagnetic interference to surrounding components, disrupting signals and threatening the proper operation of electronic devices, seriously affecting the lifespan and safety of electronic components. To address this issue, numerous measures have been implemented to prevent and control electromagnetic pollution, with the development of electromagnetic shielding materials being one of the most cost-effective means.

[0003] In recent years, lightweight, high-strength electromagnetic shielding has become increasingly common. However, current preparation technologies are complex and expensive, hindering their widespread adoption and application. Furthermore, the preparation of electromagnetic shielding materials with high shielding effectiveness, long service life, and excellent mechanical properties remains challenging, and further research is needed into their preparation methods, mechanisms, and conditions.

[0004] Layered double hydroxides (LDHs), also known as hydrotalcite-like materials, are a class of synthetic, two-dimensional nanostructured anionic clays composed of positively charged hydroxide layers bounded by negatively charged anions in the interlayer spaces. LDHs not only possess a stable layered structure but also a high aspect ratio, high specific surface area, and abundant interlayer interfaces. Furthermore, LDHs exhibit certain electronic conductivity properties. These properties make LDHs well-suited for use as fillers in polymer-based electromagnetic shielding composites.

[0005] Currently, researchers mainly prepare polymer-based electromagnetic shielding materials by blending a polymer matrix with functional fillers. However, simple blending has certain limitations. For example, when the amount of functional filler is low, the randomly dispersed functional fillers cannot form a good conductive network, which reduces the electromagnetic interference shielding performance of the polymer-based composite film. When the filler amount is high, although the electromagnetic shielding performance is improved, it also brings a series of new problems such as processing difficulties and poor mechanical properties. Therefore, a reasonable preparation process is used to solve the problems of the blending method. Since inorganic fillers do not have self-filming properties, many researchers often use cross-linking agents to deposit functional fillers on the surface of the polymer film by vacuum filtration to solve the problem of poor dispersion of functional fillers in the polymer matrix. However, this method also has problems such as poor bonding between the deposited layer and the polymer matrix and easy peeling during use.

[0006] Although LDH has good properties, when it is directly used in the preparation of electromagnetic shielding film, there is a problem that inorganic nanomaterials cannot form films independently, and it is difficult to make films by direct application. Therefore, it is necessary to provide a new LDH electromagnetic shielding film to solve the above problems. Summary of the Invention

[0007] In order to solve the above problems, the present invention provides an application of LDH / polymer in the preparation of electromagnetic shielding film.

[0008] This is achieved specifically through the following technical solutions:

[0009] 1. An application of LDH / polymer in the preparation of an electromagnetic shielding film, wherein the preparation method of the electromagnetic shielding film comprises the following steps:

[0010] S1: Add solvent to the LDH / polymer solution and mechanically stir for 0.5-2h. After the LDH / polymer is completely settled, pour out the supernatant and degas to obtain the LDH / polymer casting solution;

[0011] S2: At room temperature, the LDH / polymer casting solution was scraped onto the nonwoven surface at a speed of 0.1-5.0 m / s;

[0012] S3: solidifying the LDH film obtained in S2 in air at room temperature to obtain an LDH electromagnetic shielding film with a thickness of 100-400 μm.

[0013] Furthermore, the preparation method of the LDH / polymer solution is:

[0014] S1: dissolving a divalent metal ion salt and a trivalent metal ion salt in water to obtain a mixed metal salt solution;

[0015] S2: Use alkaline solution to adjust the pH value during the reaction so that the pH value of the system does not exceed 10;

[0016] S3: After pH adjustment, add the polymer and stir for 1-6 hours to obtain the LDH / polymer solution.

[0017] Furthermore, the polymer is a low molecular weight polymer with a molecular weight of 550-5500 and a styrene / maleic anhydride copolymer with a maleic anhydride content of 25-50%.

[0018] Furthermore, the divalent metal ion in the divalent metal ion salt is a divalent metal ion that can generate hydroxide, specifically Mg 2+ 、Co 2+ 、Ni 2+ 、Zn 2+ 、Cu 2+ 、Mn 2+ , Ca2+ One or more of the following; the trivalent metal ion in the trivalent metal ion salt is a trivalent metal ion that can generate hydroxide, specifically Al 3+ 、Fe 3+ 、Co 3+ Cr 3+ 、Ga 3+ One or more of the following; the anion in the mixed metal ion salt solution is NO 3- The molar ratio of divalent metal ions to trivalent metal ions is (2-5):1; the mass ratio of trivalent metal ion salt to the polymer is 1:(1-7).

[0019] Furthermore, the reaction temperature in step S2 is 25-80° C., and the alkaline solution is sodium hydroxide solution or potassium hydroxide solution.

[0020] Furthermore, the solvent is a water-soluble solvent, such as one of methanol, ethanol, propanol, and DMAc; and the volume ratio of the LDH / polymer complex solution to the solvent is 1-0.2:1.

[0021] Furthermore, the nonwoven fabric is polyethylene terephthalate or polyamide nonwoven fabric, and has a thickness of 50-150 μm.

[0022] In summary, the beneficial effects of the present invention are as follows: a polymer that can obtain a polymer salt under alkaline conditions is used as a membrane-forming polymer material, and has the property of being soluble in water but insoluble in solvents; after the pH control is completed by co-precipitation method to prepare LDH, LDH is in the nucleation and growth stage, and then the polymer is introduced. At this time, part of the polymer can be connected with LDH by hydrogen bonds to surround the LDH layer plates, thereby improving the binding between the polymer and LDH and avoiding the problem of LDH peeling off in the polymer matrix; part of the polymer exists in an aqueous solution, and then a certain water-soluble solvent is added to obtain an aqueous phase / solvent phase solution, and the property of the polymer salt being soluble in water but insoluble in solvents is used to precipitate the polymer from the aqueous solution, and the precipitated polymer is deposited on the surface of the LDH layer plates, and the polymer chains deposited on the surface of the LDH layer plates are bound to the LDH layer plates in the aqueous phase. The polymer chains are entangled with each other, wrapping the LDH layers, and under the action of gravity, the LDH settles in the solution. The more polymer precipitates, the more polymer wraps the LDH layers, avoiding the stacking between the LDH layers and making the LDH evenly dispersed in the polymer. In addition, the mutual entanglement between the polymer chains makes the LDH / polymer ductile and has the characteristics of film formation; mechanical stirring is carried out for 0.5-2 hours, and after the LDH / polymer is completely settled, the supernatant is poured out and fully degassed to obtain a flowable LDH / polymer casting liquid; finally, a surface coating method is used to coat the non-woven fabric surface to form a film, solving the problem that inorganic nanoparticle materials cannot form films independently; by controlling the amount and time of solvent addition, the ratio of LDH / polymer is adjusted to prepare LDH films with different electromagnetic shielding properties.

[0023] The following conditions are required to prepare the above electromagnetic shielding film:

[0024] (1) The polymer can react under alkaline conditions to obtain a polymer salt that is soluble in water but insoluble in solvents;

[0025] (2) The polymer salt can become the interlayer anion of LDH through charge compensation;

[0026] (3) Moderate polymer content. On the one hand, too low a content will result in poor casting fluidity and poor scraping effect. On the other hand, an appropriate amount of polymer ensures uniform dispersion of LDH, resulting in a casting fluid with good scraping effect.

[0027] This patent utilizes film-forming technology to produce an LDH electromagnetic shielding film for use in the electromagnetic shielding field. The introduction of the dielectric material LDH helps improve the dielectric loss of the composite film, thereby obtaining a membrane material with electromagnetic shielding properties. Furthermore, the strong interaction between the dielectric material LDH and the polymer is utilized to not only solve the problem of inorganic nanoparticles being easily detached from the polymer matrix, but also to create more interfaces, generating interfacial polarization, which is beneficial for improving electromagnetic shielding performance. The preparation process of this invention is simple, environmentally friendly, produces few by-products, and can reduce industrialization costs. DETAILED DESCRIPTION

[0028] The specific embodiments of the present invention are further described in detail below, but the present invention is not limited to these embodiments. Any improvement or replacement based on the basic spirit of the present embodiment still falls within the scope of protection required by the claims of the present invention.

[0029] Example 1

[0030] 1. Dissolve 9.6 g of magnesium nitrate and 4.7 g of aluminum nitrate in 30 ml of deionized water to obtain a mixed metal salt solution;

[0031] 2. Adjust the pH value of the mixed metal salt solution with 4 mol / L NaOH solution at room temperature so that the pH value of the system does not exceed 10;

[0032] 3. After pH adjustment, 32.9 g of styrene maleic anhydride copolymer was dispersed in the mixed solution and stirred at room temperature for 6 h to obtain a MgAlLDH / polymer solution;

[0033] 4. Add 100 ml of ethanol dropwise to the MgAlLDH / polymer solution and stir mechanically for 0.5 h. Pour off the supernatant and degas thoroughly to obtain the MgAlLDH / polymer casting solution.

[0034] 5. Under room temperature, the MgAlLDH / polymer casting solution was scraped onto the surface of a woven fabric with a thickness of 50 μm at a speed of 0.1 m / s to obtain an LDH film;

[0035] 6. The obtained LDH film body is solidified and formed in air at room temperature to obtain an LDH electromagnetic shielding film with a film thickness of 70 μm.

[0036] Example 2

[0037] 1. Dissolve 10.1 g of cobalt nitrate and 5.0 g of ferric nitrate in 50 ml of deionized water to obtain a mixed metal salt solution;

[0038] 2. Adjust the pH value of the mixed metal salt solution with 4 mol / L NaOH solution at 60°C so that the pH value of the system does not exceed 10;

[0039] 3. After pH adjustment, 15 g of styrene maleic anhydride copolymer was dispersed into the above mixed solution and stirred at 60°C for 3 h to obtain a CoFeLDH / polymer solution;

[0040] 4. Add 150 ml of methanol to the CoFeLDH / polymer solution and stir mechanically for 2 hours. Pour off the supernatant and degas thoroughly to obtain the CoFeLDH / polymer casting solution.

[0041] 5. Under room temperature, the CoFeLDH / polymer casting solution was scraped onto the surface of a 50 μm nonwoven fabric at a speed of 5 m / s to obtain an LDH film;

[0042] 6. The obtained LDH film body is solidified and formed in air at room temperature to obtain an LDH electromagnetic shielding film with a film thickness of 90 μm.

[0043] Example 3

[0044] 1. Dissolve 7.23 g of nickel nitrate and 5 g of ferric nitrate in 50 ml of deionized water to obtain a mixed metal salt solution;

[0045] 2. Adjust the pH value of the mixed metal salt solution with 4 mol / L NaOH solution at 70°C so that the pH value of the system does not exceed 10;

[0046] 3. After pH adjustment, 5 g of styrene / maleic anhydride copolymer was dispersed into the above mixed solution and stirred at 70°C for 3 h to obtain a NiFeLDH / polymer solution;

[0047] 4. Add 100 ml of acetone dropwise to the NiFeLDH / polymer solution and stir mechanically for 1 hour. Pour off the supernatant and degas thoroughly to obtain the NiFeLDH / polymer casting solution.

[0048] 5. Under room temperature, the NiFeLDH / polymer casting solution was scraped onto the surface of the nonwoven fabric at a speed of 2 m / s to obtain an LDH film;

[0049] 6. The obtained LDH film body is solidified and formed in air at room temperature to obtain an LDH electromagnetic shielding film with a film thickness of 80 μm.

[0050] Example 4

[0051] 1. Dissolve 14.9 g of magnesium nitrate and 5 g of ferric nitrate in 50 ml of deionized water to obtain a mixed metal salt solution;

[0052] 2. Adjust the pH value of the mixed metal salt solution with 4 mol / L NaOH solution at room temperature so that the pH value of the system does not exceed 10;

[0053] 3. After pH adjustment, 20 g of styrene / maleic anhydride copolymer was dispersed into the above mixed solution and stirred at 70°C for 1 hour to obtain a NiFeLDH / polymer solution;

[0054] 4. Add 120 ml of DMAc dropwise to the ZnFeLDH / polymer solution and stir mechanically for 1.5 h. Pour off the supernatant and degas thoroughly to obtain the ZnFeLDH / polymer casting solution.

[0055] 5. Under room temperature, the MgAlLDH / polymer casting solution was scraped onto the surface of the nonwoven fabric at a speed of 3 m / s to obtain an LDH film;

[0056] 6. The obtained LDH film body is solidified and formed in air at room temperature to obtain an LDH electromagnetic shielding film with a film thickness of 80 μm.

[0057] Example 5

[0058] 2. Dissolve 15.1 g of copper nitrate and 5 g of ferric nitrate in 50 ml of deionized water to obtain a mixed metal salt solution;

[0059] 3. Adjust the pH value of the mixed metal salt solution with 4 mol / L NaOH solution at room temperature so that the pH value of the system does not exceed 10;

[0060] 3. After pH adjustment, 25 g of styrene / maleic anhydride copolymer was dispersed into the above mixed solution and stirred at 70°C for 2 h to obtain a NiFeLDH / polymer solution;

[0061] 4. Add 80 ml of ethanol dropwise to the CuFeLDH / polymer solution and stir mechanically for 0.5 h. Pour off the supernatant and degas thoroughly to obtain the CuFeLDH / polymer casting solution.

[0062] 5. Under room temperature, the CuFeLDH / polymer casting solution was scraped onto the surface of the nonwoven fabric at a speed of 0.1 m / s to obtain an LDH film;

[0063] 6. The obtained LDH film body is solidified in air at room temperature to obtain an LDH electromagnetic shielding film with a film thickness of 100 μm.

[0064] Comparative Example 1

[0065] The LDH / polymer was prepared by the method of Example 2, except that the solution after the reaction was centrifuged, the precipitate obtained after centrifugation was washed with deionized water until neutral, dried in a drying oven, and then ground into powder, and finally compressed into samples using a tablet press.

[0066] 1. LDH membrane performance test

[0067] 1.1 Experimental Materials

[0068] Electromagnetic shielding films were prepared using the methods of Examples 1-5 and Comparative Example 1.

[0069] 1.2 Experimental methods

[0070] The conductive properties of the film were tested using a four-probe resistivity tester (ST2258C multifunctional digital four-probe tester, Suzhou Jingge Electronics Co., Ltd.).

[0071] The electromagnetic shielding performance of the membrane was tested using a vector network analyzer (Agilent E5071C) using the coaxial method.

[0072] The electrical conductivity and electromagnetic shielding performance of the electromagnetic shielding film were tested, and the results are shown in Table 1.

[0073] 1.3 Experimental Results

[0074] Table 1

[0075]

[0076] The experiment shows that the electrical conductivity and electromagnetic shielding performance of the pressed sample are similar to those of Example 2, but its mechanical properties are much worse than those of Example 2.

[0077] 2. Screening Experiment

[0078] 2.1 Experimental Materials

[0079] Sample 1: The LDH electromagnetic shielding film was prepared by the method of Example 2, except that the type of metal cations was different, and the divalent metal ion was Cu 2+ .

[0080] Sample 2: The LDH electromagnetic shielding film was prepared by the method of Example 2, except that the amount of solvent used was different, and the content of methanol was 100 ml.

[0081] Sample 3: The LDH electromagnetic shielding film was prepared by the method of Example 2, except that the stirring time and the mechanical stirring time were 0.5 h.

[0082] Sample 4: The LDH electromagnetic shielding film was prepared by the method of Example 2, except that the solvent type was different, and the solvent used was DMAc.

[0083] 2.2 Experimental methods

[0084] The conductivity and electromagnetic shielding performance of samples 1-4 were measured using the same method as in 1.2. The results are shown in Table 2.

[0085] 2.3 Experimental Results

[0086] Table 2

[0087] Example Conductivity / (S / m) Electromagnetic shielding performance (EMI SE) Sample 1 <![CDATA[2.00x10 -6 ]]> 0.71dB Sample 2 <![CDATA[1.86x10 -6 ]]> 0.83dB Sample 3 <![CDATA[1.77x10 -6 ]]> 0.79dB Sample 4 <![CDATA[2.03x10 -6 ]]> 0.88dB

[0088] From the experimental results, we can see that sample 1 changes the divalent metal ion to Cu 2+, the conductivity did not change much, but the electromagnetic shielding performance decreased. Sample 2 reduced the amount of solvent used, which reduced the amount of polymer salt deposited on the LDH surface, and both the conductivity and electromagnetic shielding performance decreased. Sample 3 reduced the mechanical stirring time, which shortened the time for polymer salt precipitation, also reducing the amount of polymer salt deposited on the LDH surface, and also reduced the conductivity and electromagnetic shielding performance. Sample 4 changed the solvent type, with minimal changes in conductivity and electromagnetic shielding performance. These results indicate that higher solvent content or longer stirring time are conducive to better electromagnetic shielding performance. In addition, the type of metal ion also has a significant impact on electromagnetic shielding performance.

Claims

1. An application of LDH / polymer in the preparation of electromagnetic shielding film, characterized in that: The preparation method of the electromagnetic shielding film comprises the following steps: S1: Add solvent to the LDH / polymer solution and mechanically stir for 0.5-2h. After the LDH / polymer is completely settled, pour out the supernatant and degas to obtain the LDH / polymer casting solution; The preparation method of the LDH / polymer solution is: (1): dissolving a divalent metal ion salt and a trivalent metal ion salt in water to obtain a mixed metal salt solution; (2): Use alkaline solution to adjust the pH value during the reaction so that the pH value of the system does not exceed 10; (3): After pH adjustment, add the polymer and stir for 1-6 hours to obtain the LDH / polymer solution; The solvent is a water-soluble solvent, specifically one of methanol, ethanol, propanol, and DMAc; the volume ratio of the LDH / polymer complex solution to the solvent is 1-0.2:1; The polymer is a low molecular weight polymer with a molecular weight of 550-5500 and a styrene / maleic anhydride copolymer with a maleic anhydride content of 25-50%; S2: At room temperature, the LDH / polymer casting solution was scraped onto the nonwoven surface at a speed of 0.1-5.0 m / s; S3: solidifying the LDH film obtained in S2 in air at room temperature to obtain an LDH electromagnetic shielding film with a thickness of 100-400 μm.

2. The use of an LDH / polymer according to claim 1 in preparing an electromagnetic shielding film, characterized in that: The divalent metal ion in the divalent metal ion salt is a divalent metal ion that can generate hydroxide, specifically Mg 2+ 、Co 2+ 、Ni 2+ 、Zn 2+ 、Cu 2+ 、Mn 2+ , Ca 2+ One or more of the following; the trivalent metal ion in the trivalent metal ion salt is a trivalent metal ion that can generate hydroxide, specifically Al 3+ 、Fe 3+ 、Co 3+ Cr 3+ 、Ga 3+ One or more of the following; the anion in the mixed metal salt solution is NO 3- The molar ratio of divalent metal ions to trivalent metal ions is (2-5):1; the mass ratio of trivalent metal ion salt to the polymer is 1:(1-7).

3. The use of an LDH / polymer according to claim 1 in preparing an electromagnetic shielding film, characterized in that: The reaction temperature in step S1 (2) is 25-80° C., and the alkaline solution is sodium hydroxide solution or potassium hydroxide solution.

4. The use of an LDH / polymer in preparing an electromagnetic shielding film according to claim 1, characterized in that: The nonwoven fabric is polyethylene terephthalate or polyamide nonwoven fabric, and has a thickness of 50-150 μm.

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