A method for preparing screen printing ink for surface protection of printed circuit boards

Abstract

This invention discloses a method for preparing a protective screen printing ink for printed circuit boards. The method includes: adding sodium dodecylbenzenesulfonate, a surfactant, to an aqueous solution of carbon nanofibers; ultrasonically dispersing the mixture; then adding it dropwise to anhydrous ethanol containing tetrabutyl titanate; magnetically stirring the mixture at room temperature until homogeneous; transferring the mixture to a reaction vessel for hydrothermal reaction for 10-12 hours; washing the mixture 4-5 times with deionized water and anhydrous ethanol; drying the resulting solid to obtain TiO2-CNF modified inorganic pigment nanoparticles; adding polydimethylsiloxane and an appropriate amount of curing agent to a hexane solution; reacting the solution at room temperature with magnetic stirring; adding a certain amount of TiO2-CNF modified inorganic pigment nanoparticles; and ultrasonically dispersing the mixture for 20-40 minutes to obtain the final liquid ink. The conductive ink prepared by this invention provides waterproof, stain-resistant, and UV-resistant protection for the surface of the printed circuit board while maintaining normal conductivity.

Description

Technical Field

[0001] This invention belongs to the field of ink technology and relates to a method for preparing a protective screen printing ink for printed circuit board surfaces. Background Technology

[0002] Printed circuit boards (PCBs) are crucial electronic components, indispensable in almost every electronic device. However, the following problems often arise during the use of PCBs:

[0003] 1. In high humidity environments, PCBs easily absorb moisture from the air. Moisture intrusion can lead to a decrease in the insulation performance of the circuit board, causing faults such as short circuits; moreover, moisture may also react chemically with the metal components on the circuit board, accelerating metal corrosion, such as the oxidation of copper lines, which seriously affects the reliability and lifespan of the PCB.

[0004] 2. In certain special operating environments, PCBs may come into contact with various chemicals, such as acids, alkalis, and organic solvents. These chemicals may corrode the surface materials of the PCB, damage its protective structure, and thus affect the performance of the circuitry. For example, in the manufacturing process of electronic devices, some chemical cleaning agents may be used. If the PCB is not properly protected during the cleaning process, it is easily corroded by these chemicals.

[0005] 3. When flexible printed circuit boards are used outdoors, they are exposed to strong ultraviolet radiation. Prolonged exposure to sunlight will cause the substrate, cover film and other materials of the circuit board to gradually age, yellow and become brittle, reducing the insulation performance and mechanical strength of the materials and shortening the service life of the circuit board.

[0006] 4. Printed circuit boards (PCBs) typically require good conductivity during normal operation, but some surface protective coatings inherently possess a certain level of resistance. For example, conformal coatings form an insulating film after drying. While their primary purpose is to provide waterproofing, moisture protection, and corrosion resistance, this film can increase the resistance between circuits, thus affecting conductivity. This effect may be more pronounced if the coating is uneven or excessively thick. If the PCB surface protection method negatively impacts the conductive transfer efficiency between the PCB and electronic components, then the consequences outweigh the benefits. Summary of the Invention

[0007] To address the aforementioned technical problems, the present invention aims to prepare a conductive ink that can be screen-printed, enabling it to achieve normal conductivity while providing waterproof (superhydrophobic), stain-resistant (self-cleaning), and UV-resistant protection for the surface of printed circuit boards.

[0008] To address the aforementioned technical problems, this invention proposes a method for preparing a protective screen printing ink for printed circuit board surfaces, comprising: Step 1, dissolving tetrabutyl titanate (TBT) in anhydrous ethanol solution to obtain a first solution; Step 2, preparing an aqueous solution of carbon nanofibers (CNF), adding the surfactant sodium dodecylbenzenesulfonate (SDBS) to the aqueous solution of carbon nanofibers, and then ultrasonically dispersing to obtain a second solution; Step 3, adding the second solution dropwise to the first solution and magnetically stirring at room temperature to mix evenly to obtain a third solution; Step 4, transferring the third solution to a reaction vessel for hydrothermal reaction for 10-12 hours, followed by treatment with deionized water and anhydrous ethanol. The solid was washed 4-5 times by centrifugation with alcohol, and then dried to obtain TiO2-CNF modified inorganic pigment nanoparticles; in step 5, polydimethylsiloxane (PDMS) and an appropriate amount of curing agent were added to the hexane solution and reacted at room temperature for 1 hour under magnetic stirring to obtain the fourth solution; in step 6, a certain amount of TiO2-CNF modified inorganic pigment nanoparticles were added to the fourth solution and ultrasonically dispersed for 20-40 minutes to obtain the final liquid TiO2-CNF-PDMS ink; wherein, the amount of TiO2-CNF modified inorganic pigment nanoparticles added in step 6 was 6wt%-10wt%.

[0009] Furthermore, the mass fraction of tetrabutyl titanate added in step 1 is 5 wt%.

[0010] Furthermore, in step 2, the aqueous solution of carbon nanofibers (CNF) has a mass fraction of 0.2 wt%; the mass ratio of sodium dodecylbenzenesulfonate (SDBS) to carbon nanofibers (CNF) is 4:5; the ultrasonic power is 120W-150W, and the ultrasonic time is 20min-40min.

[0011] Furthermore, the mass ratio of anhydrous ethanol to deionized water added in step 4 is 2:1.

[0012] Furthermore, the mass fraction of polydimethylsiloxane added in step 5 is 9%, and the mass ratio between hexane, polydimethylsiloxane and curing agent is 100:10:1.

[0013] Furthermore, the ultrasonic power during ultrasonic dispersion in step 6 is 120W-150W.

[0014] Furthermore, this invention also proposes a method for preparing a printed circuit board using the screen printing ink described above, comprising: step 1', preparing a screen printing stencil; step 2', adjusting the alignment so that the pattern of the screen printing stencil is aligned with the surface protection area of ​​the flexible printed circuit board; step 3', uniformly printing the liquid TiO2-CNF-PDMS ink prepared above onto the surface protection area of ​​the flexible printed circuit board through the apertures of the screen printing stencil; step 4', placing the printed printed circuit board into a drying device and baking it at 70-90 degrees Celsius for 80-100 minutes.

[0015] Furthermore, in step 1', the screen printing stencil is made using nylon mesh as the mesh fabric.

[0016] Furthermore, the alignment adjustment in step 2', which ensures that the pattern on the screen printing stencil is aligned with the surface protection area of ​​the flexible printed circuit board, specifically includes: after the screen printing stencil is made, alignment adjustment is performed, that is, adjusting the relative position of the screen printing stencil and the flexible printed circuit board so that the pattern on the screen printing stencil is aligned with the surface protection area of ​​the flexible printed circuit board, thereby ensuring that the liquid ink is printed and coated on the surface protection area of ​​the flexible printed circuit board without coating other areas.

[0017] The liquid TiO2-CNF-PDMS ink prepared by the method of this invention can be printed on the surface of printed circuit boards by screen printing, which can make the surface of printed circuit boards waterproof, self-cleaning and UV resistant, thereby expanding the application scenarios of printed circuit boards.

[0018] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and are not intended to limit this disclosure. Attached Figure Description

[0019] The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments consistent with this disclosure and, together with the description, serve to explain the principles of this disclosure.

[0020] Figure 1 A schematic flowchart of the method for preparing protective screen printing ink for printed circuit board surfaces according to the present invention is shown;

[0021] Figure 2 A scanning electron microscope image of TiO2-CNF modified inorganic pigment nanoparticles according to an embodiment of the present invention is shown.

[0022] Figure 3 The X-ray diffraction pattern of anatase phase titanium dioxide JCPDS standard card and CNF-TiO2 modified inorganic pigment nanoparticles according to an embodiment of the present invention is shown.

[0023] Figure 4This diagram illustrates a process flow diagram of the method for preparing printed circuit boards using the prepared screen printing ink of the present invention. Detailed Implementation

[0024] The present invention will be further described in detail below with reference to specific embodiments and accompanying drawings. The described embodiments are only some embodiments of the present invention, not all of them. The following embodiments are only for more clearly illustrating the technical solutions of the present invention and should not be used to limit the scope of protection of the present invention.

[0025] like Figure 1 As shown, this invention provides a method for preparing a protective screen printing ink for printed circuit board surfaces. The method involves in-situ growth of TiO2 on the CNF surface via a hydrothermal reaction, followed by hydrophobic modification to obtain a conductive ink with superhydrophobic, self-cleaning, and UV-resistant properties. The specific steps include:

[0026] Step 1: Dissolve tetrabutyl titanate (TBT) in anhydrous ethanol solution to obtain the first solution. Anhydrous ethanol is a good solvent that can uniformly disperse TBT, providing a uniform and stable environment for the subsequent hydrolysis reaction, and can also prevent it from hydrolyzing too quickly and agglomerating when in contact with water.

[0027] In one embodiment, the mass ratio of tetrabutyl titanate (TBT) is 3.5 wt%.

[0028] Step 2: Prepare an aqueous solution of carbon nanofibers (CNF). Add sodium dodecylbenzenesulfonate (SDBS) to the CNF aqueous solution to improve the dispersibility of carbon nanofibers. Then, ultrasonic dispersion further enhances the dispersion effect of carbon nanofibers, ensuring that carbon nanofibers exist in the solution in a uniform state, thus obtaining a second solution.

[0029] In a preferred embodiment, the aqueous solution of carbon nanofibers (CNF) has a mass fraction of 0.2 wt%; the mass ratio of sodium dodecylbenzenesulfonate (SDBS) to carbon nanofibers (CNF) is 4:5.

[0030] Step 3: The second solution is added dropwise to the first solution, and the mixture is magnetically stirred at room temperature to obtain a third solution. This dropwise addition allows tetrabutyl titanate to slowly contact the carbon nanofibers, preventing excessively high local concentrations of tetrabutyl titanate that could lead to rapid hydrolysis and the formation of large particles. Furthermore, thorough stirring ensures complete mixing of the two solutions, allowing the tetrabutyl titanate to uniformly coat the surface of the carbon nanofibers, which is beneficial for the subsequent formation of uniform TiO2-CNF modified inorganic pigment nanoparticles.

[0031] Step 4: Transfer the third solution to the reaction vessel and react hydrothermally for 10-12 hours. Then, wash the solution 4-5 times with deionized water and anhydrous ethanol by centrifugation. Dry the obtained solid to obtain TiO2-CNF modified inorganic pigment nanoparticles.

[0032] In one embodiment, the ratio of anhydrous ethanol to deionized water is 2:1. This ratio is crucial for controlling the hydrolysis rate of tetrabutyl titanate. Ethanol reduces the reactivity of water, resulting in a moderate hydrolysis rate of tetrabutyl titanate, which is beneficial for forming uniformly sized and well-dispersed TiO nanoparticles. If the water ratio is too high, tetrabutyl titanate may hydrolyze rapidly, leading to particle aggregation; if the ethanol ratio is too high, the hydrolysis reaction may be too slow, affecting reaction efficiency.

[0033] Step 5: Polydimethylsiloxane (PDMS) and PDMS curing agent are added to a hexane solution and reacted at room temperature for 1 hour under magnetic stirring to obtain the fourth solution. Hexane, as a solvent, provides a suitable environment for the reaction between PDMS and the curing agent.

[0034] In one embodiment, the mass fraction of polydimethylsiloxane is 9%, and the mass ratio of hexane, polydimethylsiloxane, and PDMS curing agent is 100:10:1. It should be noted that a suitable polydimethylsiloxane ratio can provide good flexibility and stability, and the ratio of curing agent to polydimethylsiloxane ensures that the polydimethylsiloxane can be fully cured to form a matrix with certain strength and properties.

[0035] Step 6: Add a certain amount of TiO2-CNF modified inorganic pigment nanoparticles to the fourth solution and ultrasonically disperse them for 20-40 minutes to obtain the final liquid TiO2-CNF-PDMS ink. Ultrasonic dispersion ensures that the TiO2-CNF modified inorganic pigment nanoparticles are uniformly dispersed in the polydimethylsiloxane solution, thereby forming a uniform and stable liquid ink, which is beneficial for subsequent printing or coating applications.

[0036] In one embodiment, the amount of TiO2-CNF modified inorganic pigment nanoparticles added is 6wt%-10wt%. By adding TiO2-CNF modified inorganic pigment nanoparticles within this specific range, the ink can have good optical and electrical properties, while ensuring the ink's flowability and printability.

[0037] Figure 2 The image shows a scanning electron microscope (SEM) image of the TiO2-CNF modified inorganic pigment nanoparticles prepared according to the present invention. It can be seen that titanium dioxide nanoparticles were successfully grown in situ on the CNF surface.

[0038] like Figure 3The X-ray diffraction test pattern shown, when compared with the JCPDS standard card (No. 21-1272), indicates that all samples are within the range of 2... The diffraction peaks at 25.3°, 37.8°, 48°, 53.9°, and 62.7° correspond to the (101), (004), (200), (105), and (204) crystal planes of anatase TiO2, respectively. No other impurity peaks were found, indicating that the samples grown on the surface of carbon nanofibers are all anatase TiO2, proving the successful generation of anatase-type titanium dioxide nanoparticles.

[0039] The liquid TiO2-CNF-PDMS ink prepared by the method of this invention can be printed on the surface of printed circuit boards by screen printing, thereby giving the surface of the printed circuit boards waterproof, self-cleaning and UV resistant functions, thus broadening the application scenarios of printed circuit boards.

[0040] In addition, such as Figure 4 As shown, the present invention further proposes a method for preparing a printed circuit board using the screen printing ink described above, comprising:

[0041] Step 1': Create a screen printing stencil.

[0042] In one embodiment, nylon mesh can be used as the mesh fabric, and a screen printing plate consistent with the surface protection area of ​​the printed circuit board can be prepared according to existing screen printing plate manufacturing methods. Alternatively, other commonly used mesh fabric materials can be selected, such as polyester mesh fabric or stainless steel mesh fabric. It should be noted that the mesh size can also be selected according to actual usage needs, as long as the printing effect of liquid TiO2-CNF-PDMS ink on the circuit board meets the requirements.

[0043] Step 2': Alignment adjustment, ensuring the pattern on the screen printing stencil is aligned with the surface protection area of ​​the flexible printed circuit board.

[0044] After the screen printing stencil is made, the next step is to adjust the alignment, that is, to adjust the relative position of the screen printing stencil and the flexible printed circuit board, so that the pattern of the screen printing stencil is aligned with the surface protection area of ​​the flexible printed circuit board, so as to ensure that the liquid ink is printed and coated on the surface protection area of ​​the flexible printed circuit board and is not coated on other areas.

[0045] Step 3': The screen printing ink prepared above is uniformly printed onto the surface protection area of ​​the flexible printed circuit board through the apertures of the screen printing stencil.

[0046] The liquid TiO2-CNF-PDMS ink prepared above was coated onto a 220-300 mesh self-made screen printing plate. The TiO2-CNF-PDMS ink was manually coated with a polyurethane right-angle squeegee to ensure that the liquid ink was evenly coated onto the surface protection area of ​​the flexible printed circuit board.

[0047] In one embodiment, the right-angle squeegee has a hardness of 65HA-70HA. Squeegees with this hardness can withstand a certain amount of pressure during screen printing without excessive deformation. When the squeegee moves across the screen and applies pressure, the moderate hardness ensures that the pressure is evenly distributed across the entire printing area. This helps the ink to be evenly transferred through the screen to the surface of the printed circuit board, avoiding problems such as inconsistent ink thickness, blurred or incomplete local patterns caused by uneven pressure, thus ensuring the integrity and clarity of the printed pattern. Furthermore, this hardness range allows the squeegee to maintain good wear resistance and deformation resistance during frequent printing operations. Compared to squeegees that are too soft, they are less prone to rapid wear or deformation during use; compared to squeegees that are too hard, they reduce damage to the screen printing plate, thereby extending the squeegee's lifespan and reducing production costs while ensuring printing quality.

[0048] In another embodiment, the squeegee is made of polyurethane. Due to the excellent elasticity and flexibility of polyurethane, the squeegee can better conform to the shape of the screen printing plate and the printed circuit board surface when in contact. Even if there are minor unevennesses on the circuit board surface or a certain degree of elastic deformation of the screen, the squeegee can adjust itself to ensure uniform ink application, reducing defects such as missed prints and incomplete prints. Furthermore, polyurethane squeegees have good chemical stability, resisting the erosion of various chemicals in screen printing inks. During prolonged contact with ink, they will not dissolve, swell, or deteriorate due to solvents, additives, or other components in the ink, ensuring the stability of the squeegee's performance and thus guaranteeing consistent printing quality.

[0049] In another embodiment, the length of the squeegee is 2.5-4.3 cm longer on each side than the width of the pattern on the screen printing stencil.

[0050] Step 4': Place the printed circuit board into the drying device and bake it at 70-90 degrees Celsius for 80-100 minutes.

[0051] The present invention will be further described in detail below through specific preferred embodiments, but the present invention is not limited to the following embodiments. Example 1

[0052] A method for preparing a protective screen printing ink for printed circuit board surfaces is specifically implemented according to the following steps: 5 wt% TBT is dissolved in anhydrous ethanol solution to obtain solution 1; a 0.5 wt% CNF aqueous solution is prepared, and 0.4 wt% SDBS is added to improve the dispersibility of CNF; then, the solution is ultrasonically dispersed to obtain solution 2; solution 2 is then added dropwise to anhydrous ethanol solution 1 containing TBT and magnetically stirred at room temperature to obtain solution 3; finally, solution 3 is transferred to a reaction vessel for hydrothermal reaction for 10-12 hours, followed by centrifugal washing with deionized water and anhydrous ethanol 4-5 times; the resulting solid is dried in a vacuum oven for 10-12 hours to obtain TiO2-CNF modified inorganic pigment nanoparticles. 10 wt% PDMS and 1 wt% curing agent were added to a hexane solution and reacted at room temperature for 1 h under magnetic stirring to obtain solution 4. 6 wt% TiO2 / CNF modified inorganic pigment nanoparticles were added to solution 4 and ultrasonically dispersed for 20 min-40 min to obtain liquid TiO2-CNF-PDMS ink. Example 2

[0053] A method for preparing a protective screen printing ink for printed circuit board surfaces is specifically implemented according to the following steps: 5 wt% TBT is dissolved in anhydrous ethanol solution to obtain solution 1; a 0.5 wt% CNF aqueous solution is prepared, and 0.4 wt% SDBS is added to improve the dispersibility of CNF; then, the solution is ultrasonically dispersed to obtain solution 2; solution 2 is then added dropwise to anhydrous ethanol solution 1 containing TBT and magnetically stirred at room temperature to obtain solution 3; finally, solution 3 is transferred to a reaction vessel for hydrothermal reaction for 10-12 hours, followed by centrifugal washing with deionized water and anhydrous ethanol 4-5 times; the resulting solid is dried in a vacuum oven for 10-12 hours to obtain TiO2-CNF modified inorganic pigment nanoparticles. 10 wt% PDMS and 1 wt% curing agent were added to a hexane solution and reacted at room temperature for 1 h under magnetic stirring to obtain solution 4. 7 wt% modified inorganic pigment nanoparticles were added to solution 4 and ultrasonically dispersed for 20 min-40 min to obtain liquid TiO2-CNF-PDMS ink. Example 3

[0054] A method for preparing a protective screen printing ink for printed circuit board surfaces is specifically implemented according to the following steps: 5 wt% TBT is dissolved in anhydrous ethanol solution to obtain solution 1; a 0.5 wt% CNF aqueous solution is prepared, and 0.4 wt% SDBS is added to improve the dispersibility of CNF; then, the solution is ultrasonically dispersed to obtain solution 2; solution 2 is then added dropwise to anhydrous ethanol solution 1 containing TBT and magnetically stirred at room temperature to obtain solution 3; finally, solution 3 is transferred to a reaction vessel for hydrothermal reaction for 10-12 hours, followed by centrifugal washing with deionized water and anhydrous ethanol 4-5 times; the resulting solid is dried in a vacuum oven for 10-12 hours to obtain TiO2 / CNF modified inorganic pigment nanoparticles. 10 wt% PDMS and 1 wt% curing agent were added to a hexane solution and reacted at room temperature for 1 h under magnetic stirring to obtain solution 4. 8 wt% TiO2 / CNF modified inorganic pigment nanoparticles were added to solution 4 and ultrasonically dispersed for 20 min-40 min to obtain liquid TiO2-CNF-PDMS ink. Example 4

[0055] A method for preparing a protective screen printing ink for printed circuit board surfaces is specifically implemented according to the following steps: 5 wt% TBT is dissolved in anhydrous ethanol solution to obtain solution 1; a 0.5 wt% CNF aqueous solution is prepared, and 0.4 wt% SDBS is added to improve the dispersibility of CNF; then, the solution is ultrasonically dispersed to obtain solution 2; solution 2 is then added dropwise to anhydrous ethanol solution 1 containing TBT and magnetically stirred at room temperature to obtain solution 3; finally, solution 3 is transferred to a reaction vessel for hydrothermal reaction for 10-12 hours, followed by centrifugal washing with deionized water and anhydrous ethanol 4-5 times; the resulting solid is dried in a vacuum oven for 10-12 hours to obtain TiO2 / CNF modified inorganic pigment nanoparticles. 10 wt% PDMS and 1 wt% curing agent were added to a hexane solution and reacted at room temperature for 1 h under magnetic stirring to obtain solution 4. 9 wt% TiO2 / CNF modified inorganic pigment nanoparticles were added to solution 4 and ultrasonically dispersed for 30 min to obtain liquid TiO2-CNF-PDMS ink. Example 5

[0056] A method for preparing a protective screen printing ink for printed circuit board surfaces is implemented according to the following steps: 5 wt% TBT is dissolved in anhydrous ethanol solution to obtain solution 1; a 0.5 wt% CNF aqueous solution is prepared, and 0.4 wt% SDBS is added to improve the dispersibility of CNF; then, the solution is ultrasonically dispersed to obtain solution 2; solution 2 is then added dropwise to anhydrous ethanol solution 1 containing TBT and magnetically stirred at room temperature to obtain solution 3; finally, solution 3 is transferred to a reaction vessel for hydrothermal reaction for 10-12 hours, followed by centrifugal washing with deionized water and anhydrous ethanol 4-5 times; the resulting solid is dried in a vacuum oven for 10-12 hours to obtain TiO2 / CNF modified inorganic pigment nanoparticles. 10 wt% PDMS and 1 wt% curing agent were added to a hexane solution and reacted at room temperature for 1 h under magnetic stirring to obtain solution 4. 10 wt% TiO2 / CNF modified inorganic pigment nanoparticles were added to solution 4 and ultrasonically dispersed for 20 min-40 min to obtain liquid TiO2-CNF-PDMS ink. Example 6

[0057] A method for preparing a printed circuit board using the screen printing ink described above is specifically implemented according to the following steps:

[0058] Step 1: Using nylon mesh as the mesh fabric, prepare a screen printing plate that matches the surface protection area of ​​the printed circuit board according to the existing screen printing plate making method.

[0059] Step 2: After making the screen printing stencil, the next step is to adjust the alignment, that is, adjust the relative position of the screen printing stencil and the flexible printed circuit board so that the pattern of the screen printing stencil is directly facing the surface protection area of ​​the flexible printed circuit board. This ensures that the liquid ink is printed and coated on the surface protection area of ​​the flexible printed circuit board and is not coated on other areas.

[0060] Step 3: Apply the inks prepared in Examples 1-5 onto a self-made 220-300 mesh screen printing plate. Manually apply the TiO2-CNF-PDMS ink using a polyurethane right-angle squeegee to ensure the liquid TiO2-CNF-PDMS ink is evenly coated onto the surface protection area of ​​the flexible printed circuit board. The right-angle squeegee has a hardness of 65HA-70HA, is made of polyurethane, and its length is 2.5-4.3 cm longer on each side than the width of the pattern on the screen printing plate.

[0061] Step 4: Place the printed circuit board into the drying device and bake it at 70-90 degrees Celsius for 80-100 minutes.

[0062] The performance of the liquid TiO2-CNF-PDMS ink prepared in Examples 1-5 of the present invention was tested after being screen printed on the surface of a printed circuit board. The results are shown in Tables 1 and 2.

[0063] Table 1 Comparison of hydrophobicity test results of sample surfaces

[0064]

[0065] Table 2 Comparison of UV resistance test results for sample surfaces

[0066]

[0067] The hydrophobic properties of the prepared liquid ink, after being screen-printed onto the surface of a printed circuit board, were tested. The results, as shown in Table 1, indicate that the hydrophobic angle increases with the addition of a small amount of modified inorganic pigment nanoparticles, reaching 159° and achieving a superhydrophobic effect. With further increases in the amount of nanoparticles added, aggregation may occur, reducing the hydrophobic angle, but the surface remains superhydrophobic. Therefore, the screen-printed ink for surface protection of printed circuit boards prepared in this invention can achieve a superhydrophobic effect while also possessing good self-cleaning capabilities.

[0068] The test results of the UV resistance of the prepared liquid ink after screen printing on the surface of the printed circuit board are shown in Table 2. It can be seen that with an appropriate amount of nanoparticles, the nanoparticles are stably fixed on the surface of the flexible printed circuit board, forming a stable microstructure, which is beneficial to improving the UV absorption capacity of the printed circuit board surface, thus increasing the absorbance in the 200nm-380nm wavelength range. However, when too many nanoparticles are added, it may damage the original microstructure of the printed circuit board surface, increase the light propagation path, and thus reduce the absorption and shielding effect of UV radiation, resulting in a slight decrease in absorbance. Therefore, it can be concluded that the screen printing ink for surface protection of printed circuit boards prepared in this invention has good UV resistance and meets the performance requirements of flexible printed circuit boards for outdoor use.

[0069] In this invention, TiO2 nanoparticles can absorb ultraviolet light from sunlight, giving the ink excellent UV resistance. PDMS has low surface energy and chemical stability, providing good waterproof performance to the PCB surface and preventing moisture penetration, while also possessing a certain degree of breathability, allowing gas molecules to pass through. Under normal conditions, it does not easily react with other substances, providing good antioxidant protection for the PCB surface. PDMS also improves the adhesion between the coating surface and the circuit board, eliminating the need for an adhesive layer compared to ordinary cover films, saving time, materials, and economic costs. The cured TiO2 / CNF / PDMS film layer has flexibility and lubricity, resulting in a clean and smooth PCB surface, avoiding quality problems such as bubbles, creases, and uneven thickness that occur during the production of ordinary cover films. CNF has excellent mechanical strength and conductivity; using it as a reinforcing material in the preparation of TiO2 / CNF / PDMS ink can significantly improve the strength and wear resistance of the printed circuit board surface, while also ensuring the normal conductive transmission function of the printed circuit board.

[0070] As described above, this invention proposes a method for preparing a protective screen printing ink for printed circuit board surfaces, comprising: Step 1, dissolving tetrabutyl titanate (TBT) in anhydrous ethanol solution to obtain a first solution; Step 2, preparing an aqueous solution of carbon nanofibers (CNF), adding sodium dodecylbenzenesulfonate (SDBS) surfactant to it, and then ultrasonically dispersing it to obtain a second solution; Step 3, adding the second solution dropwise to the first solution containing tetrabutyl titanate in anhydrous ethanol and mixing it uniformly at room temperature with magnetic stirring to obtain a third solution; Step 4, transferring the third solution to a reaction vessel... After hydrothermal reaction in the reactor for 10-12 hours, the solid is washed 4-5 times by centrifugation with deionized water and anhydrous ethanol. The resulting solid is then dried to obtain TiO2-CNF modified inorganic pigment nanoparticles. In step 5, polydimethylsiloxane (PDMS) and an appropriate amount of curing agent are added to a hexane solution and reacted at room temperature for 1 hour under magnetic stirring to obtain a fourth solution. In step 6, a certain amount of TiO2-CNF modified inorganic pigment nanoparticles are added to this fourth solution and ultrasonically dispersed for 20-40 minutes to obtain the final liquid TiO2-CNF-PDMS ink. This prepared screen printing ink can be printed onto the surface of a printed circuit board (PCB) using screen printing, giving the PCB surface waterproof, self-cleaning, and UV-resistant properties, thus broadening the application scenarios of PCBs.

[0071] It should be emphasized that the embodiments described in this invention are exemplary, not limiting. Therefore, this invention is not limited to the embodiments described in the specific implementation. Any other implementation methods derived by those skilled in the art based on the technical solutions of this invention also fall within the scope of protection of this invention.

Claims

1. A method for preparing a protective screen printing ink for printed circuit board surfaces, characterized in that, include: Step 1: Dissolve tetrabutyl titanate in anhydrous ethanol solution to obtain the first solution; Step 2: Prepare an aqueous solution of carbon nanofibers by adding sodium dodecylbenzenesulfonate, a surfactant, to the aqueous solution of carbon nanofibers and then dispersing it by ultrasonication to obtain a second solution. Step 3: Add the second solution dropwise to the first solution and mix thoroughly with magnetic stirring at room temperature to obtain the third solution; Step 4: Transfer the third solution to the reaction vessel and hydrothermally react for 10-12 hours. Then, wash the solution 4-5 times with deionized water and anhydrous ethanol by centrifugation. Dry the obtained solid to obtain TiO2-CNF modified inorganic pigment nanoparticles. Step 5: Add polydimethylsiloxane and an appropriate amount of curing agent to the hexane solution and react at room temperature for 1 hour under magnetic stirring to obtain the fourth solution; Step 6: Add a certain amount of TiO2-CNF modified inorganic pigment nanoparticles to the fourth solution and perform ultrasonic dispersion for 20-40 min to obtain the final liquid TiO2-CNF-PDMS ink. In step 6, the amount of TiO2-CNF modified inorganic pigment nanoparticles added is 6wt%-10wt%.

2. The method for preparing the protective screen printing ink for printed circuit board surfaces according to claim 1, characterized in that, The mass fraction of tetrabutyl titanate added in step 1 is 5 wt%.

3. The method for preparing protective screen printing ink for printed circuit board surfaces according to claim 2, characterized in that, The mass fraction of the aqueous solution of carbon nanofibers in step 2 is 0.2 wt%; the mass ratio of sodium dodecylbenzenesulfonate to carbon nanofibers is 4:5; the ultrasonic power is 120W-150W, and the ultrasonic time is 20min-40min.

4. The method for preparing protective screen printing ink for printed circuit board surfaces according to claim 3, characterized in that, The mass ratio of anhydrous ethanol to deionized water added in step 4 is 2:

1.

5. The method for preparing protective screen printing ink for printed circuit board surfaces according to claim 4, characterized in that, The mass fraction of polydimethylsiloxane added in step 5 is 9%, and the mass ratio of hexane, polydimethylsiloxane and curing agent is 100:10:

1.

6. The method for preparing protective screen printing ink for printed circuit board surfaces according to claim 5, characterized in that, The ultrasonic power during ultrasonic dispersion in step 6 is 120W-150W.

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