Preparation method of screen printing ink for protecting surface of printed circuit board

Abstract

The invention discloses a preparation method of screen printing ink for protecting the surface of a printed circuit board, which comprises the following steps: adding a surfactant sodium dodecyl benzene sulfonate into a carbon nanofiber aqueous solution, ultrasonically dispersing, dropwise adding into absolute ethyl alcohol containing tetrabutyl titanate, magnetically stirring and uniformly mixing at room temperature, and drying to obtain the screen printing ink for protecting the surface of the printed circuit board. The preparation method comprises the following steps: taking TiO2-CNF as a raw material, transferring into a reaction kettle, carrying out hydrothermal reaction for 10-12 hours, carrying out centrifugal washing for 4-5 times by using deionized water and absolute ethyl alcohol, drying the obtained solid to obtain TiO2-CNF modified inorganic pigment nanoparticles, adding polydimethylsiloxane and a proper amount of a curing agent into an n-hexane solution, carrying out room-temperature reaction under magnetic stirring, adding a certain amount of TiO2-CNF modified inorganic pigment nanoparticles, and carrying out magnetic stirring to obtain the TiO2-CNF modified inorganic pigment nanoparticles. And carrying out ultrasonic dispersion for 20-40 minutes to obtain the final liquid ink. According to the conductive ink for silk-screen printing, the normal conductive function is realized, and meanwhile, the waterproof, anti-pollution and anti-ultraviolet protection effects on the surface of a printed circuit board are achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of inks and relates to a method for preparing a surface protective silk-screen ink for a printed circuit board. Background Art

[0002] Printed circuit board (PCB) is a very important electronic component, which is indispensable in almost every electronic device. However, the following problems often occur during the use of PCB printed circuit boards: 1. In a high humidity environment, PCBs easily absorb moisture from the air. The intrusion of moisture will cause the insulation performance of the circuit board to deteriorate, causing circuit short circuits and other faults; moreover, moisture may also react chemically with the metal components on the circuit board, accelerating the corrosion of the metal, such as the oxidation of copper circuits, seriously affecting the reliability and service life of the PCB.

[0003] 2. In some special use environments, PCB may be exposed to various chemicals, such as acid, alkali, organic solvents, etc. These chemicals may corrode the surface material of PCB, destroy its protective structure, and thus affect the performance of the circuit. For example, in the manufacturing process of electronic equipment, some chemical cleaning agents may be used. If the PCB is not properly protected during the cleaning process, it is easy to be corroded by chemicals.

[0004] 3. When flexible printed circuit boards are used outdoors, the ultraviolet radiation is strong. If exposed to sunlight for a long time, the substrate, cover film and other materials of the circuit board will gradually age, turn yellow and become brittle, reducing the insulation performance and mechanical strength of the material and shortening the service life of the circuit board.

[0005] 4. Printed circuit boards usually require good electrical conductivity in normal operation, and some surface protection coatings themselves have a certain resistance. For example, the three-conformal paint coating will form an insulating film after drying. Although its main purpose is to provide waterproof, moisture-proof and anti-corrosion protection, this film may increase the resistance between the lines, thereby having a certain impact on the conductive performance. If the coating is uneven or too thick, this effect may be more obvious. If the PCB surface protection method affects the conductive transmission efficiency between the printed circuit board and electronic components, it will not be worth the loss. Summary of the invention

[0006] In view of the above technical problems, the problem to be solved by the present invention is to prepare a conductive ink that can be screen-printed so that it can achieve normal conductive functions while providing waterproof (super-hydrophobic), anti-fouling (self-cleaning) and anti-ultraviolet protection for the surface of the printed circuit board.

[0007] In order to solve the above technical problems, the present invention proposes a method for preparing a surface protective screen printing ink for a printed circuit board, which comprises: step 1, dissolving tetrabutyl titanate (TBT) in an anhydrous ethanol solution to obtain a first solution; step 2, preparing a carbon nanofiber (CNF) aqueous solution, adding a surfactant sodium dodecylbenzene sulfonate (SDBS) to the carbon nanofiber aqueous solution, and then ultrasonically dispersing to obtain a second solution; step 3, adding the second solution dropwise to the first solution, stirring and mixing evenly at room temperature with magnetic stirring to obtain a third solution; step 4, transferring the third solution to a reactor for hydrothermal reaction for 10h-12h, and then rinsing with deionized water, anhydrous ethanol, and stirring. The mixture was centrifuged and washed with alcohol for 4-5 times, and the obtained solid was dried to obtain TiO2-CNF modified inorganic pigment nanoparticles; step 5, polydimethylsiloxane (PDMS) and an appropriate amount of curing agent were added to the n-hexane solution and reacted at room temperature for 1 hour under magnetic stirring to obtain a fourth solution; step 6, a certain amount of TiO2-CNF modified inorganic pigment nanoparticles was added to the fourth solution, and ultrasonic dispersion was performed 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 is 6wt%-10wt%.

[0008] Furthermore, the mass fraction of tetrabutyl titanate added in step 1 is 5wt%.

[0009] Furthermore, the mass fraction of the aqueous solution of carbon nanofibers (CNF) in step 2 is: 0.2wt%; the mass ratio of sodium dodecylbenzene sulfonate (SDBS) to carbon nanofibers (CNF) is 4:5; the ultrasonic power is 120W-150W, and the ultrasonic time is 20min-40min.

[0010] Furthermore, the mass ratio of anhydrous ethanol to deionized water added in step 4 is 2:1.

[0011] Furthermore, the mass fraction of the polydimethylsiloxane added in step 5 is 9%, and the mass ratio of n-hexane, polydimethylsiloxane and curing agent is 100:10:1.

[0012] Furthermore, the ultrasonic power during ultrasonic dispersion in step 6 is 120W-150W.

[0013] In addition, the present invention also proposes a method for preparing a printed circuit board using the silk screen printing ink as described above, which comprises: step 1', making a silk screen printing screen; step 2', adjusting the position so that the pattern of the silk screen printing screen is aligned with the surface protection area of ​​the flexible printed circuit board; step 3', printing the liquid TiO2-CNF-PDMS ink prepared by the above-mentioned method evenly onto the surface protection area of ​​the flexible printed circuit board through the pores of the silk screen printing screen; step 4', placing the printed printed circuit board into a drying device, adjusting the temperature of the drying device to bake at 70-90 degrees Celsius for 80-100 minutes.

[0014] Furthermore, in the step 1', a nylon screen is used as the mesh cloth for making the screen printing screen.

[0015] Furthermore, the alignment adjustment in step 2' makes the pattern of the silk screen directly opposite to the surface protection area of ​​the flexible printed circuit board, specifically including: after the silk screen is made, the alignment adjustment is performed, that is, the relative position of the silk screen and the flexible printed circuit board is adjusted, so that the pattern of the silk screen is directly opposite to 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 without being coated on other areas.

[0016] The liquid TiO2-CNF-PDMS ink prepared by the method of the present invention can be printed on the surface of a printed circuit board by screen printing to make the surface of the printed circuit board have waterproof, self-cleaning and UV resistance functions, thereby broadening the application scenarios of the printed circuit board.

[0017] It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present disclosure and, together with the description, serve to explain the principles of the present disclosure.

[0019] Figure 1 The schematic diagram of the process of preparing the screen printing ink for protecting the surface of a printed circuit board of the present invention is shown; Figure 2 A scanning electron microscope image of TiO2-CNF modified inorganic pigment nanoparticles according to an embodiment of the present invention is shown; Figure 3 The figure shows the X-ray diffraction pattern of the anatase phase titanium dioxide JCPDS standard card and the CNF-TiO2 modified inorganic pigment nanoparticles according to one embodiment of the present invention; Figure 4 The schematic diagram of the process of the method for preparing a printed circuit board by using the prepared screen printing ink of the present invention is shown. DETAILED DESCRIPTION

[0020] The present invention is further described in detail below in conjunction with specific embodiments and drawings: the described embodiments are only part of the 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 cannot be used to limit the scope of protection of the present invention.

[0021] like Figure 1 As shown, the present invention provides a method for preparing a screen printing ink for protecting the surface of a printed circuit board, which in situ grows TiO2 on the surface of CNF by a hydrothermal reaction, and then hydrophobically modifies it to obtain a conductive ink with super hydrophobic, self-cleaning and UV resistance, specifically comprising the following steps: Step 1, dissolving tetrabutyl titanate (TBT) in an anhydrous ethanol solution to obtain a first solution, wherein anhydrous ethanol, as a good solvent, can evenly disperse TBT, provide a uniform and stable environment for the subsequent hydrolysis reaction, and prevent it from agglomerating due to excessive hydrolysis when in contact with water.

[0022] In one embodiment, the mass ratio of tetrabutyl titanate (TBT) is 3.5 wt %.

[0023] Step 2, preparing a carbon nanofiber (CNF) aqueous solution, adding a surfactant sodium dodecylbenzene sulfonate (SDBS) to the CNF aqueous solution to improve the dispersibility of the carbon nanofibers, and then ultrasonic dispersion to further enhance the dispersion effect of the carbon nanofibers, ensuring that the carbon nanofibers are present in the solution in a uniform state, and obtaining a second solution.

[0024] In a preferred embodiment, the mass fraction of the aqueous solution of carbon nanofibers (CNF) is 0.2 wt %; and the mass ratio of sodium dodecylbenzene sulfonate (SDBS) to carbon nanofibers (CNF) is 4:5.

[0025] Step 3, adding the second solution dropwise to the first solution, and mixing them evenly by magnetic stirring at room temperature to obtain a third solution. The dropwise addition method can make tetrabutyl titanate slowly contact with the carbon nanofibers, avoiding excessive local concentration of tetrabutyl titanate and rapid hydrolysis to form large particles. In addition, sufficient stirring can ensure that the two solutions are fully mixed, so that tetrabutyl titanate can be evenly coated on the surface of the carbon nanofibers, which is conducive to the subsequent formation of uniform TiO2-CNF modified inorganic pigment nanoparticles.

[0026] Step 4, transferring the third solution to a reactor for hydrothermal reaction for 10h-12h, washing by centrifugation with deionized water and anhydrous ethanol for 4-5 times, and drying the obtained solid to obtain TiO2-CNF modified inorganic pigment nanoparticles.

[0027] In one embodiment, the added anhydrous ethanol and deionized water are 2:1. This ratio is crucial for controlling the hydrolysis rate of tetrabutyl titanate. Ethanol can reduce the activity of water, so that the hydrolysis rate of tetrabutyl titanate is moderate, which is conducive to the formation of TiO nanoparticles with uniform particle size and good dispersion. If the proportion of water is too high, tetrabutyl titanate may hydrolyze quickly, resulting in particle agglomeration; if the proportion of ethanol is too high, the hydrolysis reaction may be too slow, affecting the reaction efficiency.

[0028] Step 5, adding polydimethylsiloxane (PDMS) and PDMS curing agent to the n-hexane solution and reacting at room temperature for 1 hour under magnetic stirring to obtain a fourth solution. Among them, n-hexane as a solvent can provide a suitable environment for the reaction of polydimethylsiloxane and PDMS curing agent.

[0029] In one embodiment, the mass fraction of polydimethylsiloxane is 9%, and the mass ratio of n-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 polydimethylsiloxane can be fully cured to form a matrix with certain strength and performance.

[0030] Step 6, adding a certain amount of TiO2-CNF modified inorganic pigment nanoparticles to the fourth solution, and ultrasonically dispersing the nanoparticles for 20-40 minutes to obtain the final liquid TiO2-CNF-PDMS ink. The ultrasonic dispersion makes the TiO2-CNF modified inorganic pigment nanoparticles uniformly dispersed in the polydimethylsiloxane solution, thereby forming a uniform and stable liquid ink, which is beneficial to subsequent printing or coating applications.

[0031] In one embodiment, the amount of the added TiO2-CNF modified inorganic pigment nanoparticles 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 fluidity and printing performance of the ink.

[0032] Figure 2 The scanning electron microscope image of the TiO2-CNF modified inorganic pigment nanoparticles prepared by the present invention is shown, and it can be seen that titanium dioxide nanoparticles are successfully grown in situ on the CNF surface.

[0033] like Figure 3 The X-ray Diffraction test chart shown in the figure is compared with the JCPDS standard card (No.21-1272) and shows that all samples have 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. In addition, no other impurity peaks were found, which indicates that the samples grown on the surface of carbon nanofibers are all anatase TiO2, proving the successful generation of anatase titanium dioxide nanoparticles.

[0034] The liquid TiO2-CNF-PDMS ink prepared by the method of the present invention can be printed on the surface of a printed circuit board by screen printing, so that the surface of the printed circuit board has waterproof, self-cleaning and UV resistance functions, thereby broadening the application scenarios of the printed circuit board.

[0035] In addition, if Figure 4 As shown, the present invention further proposes a method for preparing a printed circuit board using the above-mentioned screen printing ink, which comprises: Step 1', making a screen printing screen.

[0036] In one embodiment, a nylon screen can be used as a mesh cloth, and a screen printing plate that is consistent with the surface protection area of ​​the printed circuit board can be prepared according to the prior art screen printing plate manufacturing method. In addition, other commonly used mesh cloth materials can also be selected, such as polyester mesh cloth, stainless steel mesh cloth, etc. It should be noted that the mesh specifications can also be selected according to actual use needs, as long as the printing effect of the liquid TiO2-CNF-PDMS ink on the circuit board meets the requirements.

[0037] Step 2', adjust the position so that the pattern of the silk screen is aligned with the surface protection area of ​​the flexible printed circuit board.

[0038] After the silk screen printing screen is made, the next step is to adjust the positioning, that is, adjust the relative position of the silk screen printing screen and the flexible printed circuit board so that the pattern of the silk screen printing screen is directly opposite to the surface protection area of ​​the flexible printed circuit board to ensure that the liquid ink is printed and coated on the surface protection area of ​​the flexible printed circuit board without coating other areas.

[0039] Step 3', printing the silk-screen printing ink prepared above evenly onto the surface protection area of ​​the flexible printed circuit board through the pores of the silk-screen screen.

[0040] The liquid TiO2-CNF-PDMS ink prepared above was coated on a 220-300 mesh homemade screen printing screen, and the TiO2-CNF-PDMS ink was manually scraped with a polyurethane right-angle scraper to evenly coat the liquid ink on the surface protection area of ​​the flexible printed circuit board.

[0041] Among them, in one embodiment, the right-angle scraper hardness is 65HA-70HA, and the scraper with this hardness can withstand a certain pressure without excessive deformation during the screen printing process. When the scraper moves on the screen printing screen to apply pressure, the moderate hardness can make the pressure evenly distributed in the entire scraping area. This helps the ink to be evenly transferred to the surface of the printed circuit board through the screen, avoiding problems such as inconsistent ink thickness, blurred or incomplete local patterns caused by uneven pressure, and ensuring the integrity and clarity of the printed pattern. In addition, this hardness range enables the scraper to maintain good wear resistance and deformation resistance during frequent scraping operations. Compared with a scraper that is too soft, it is not easy to wear or deform quickly during use; compared with a scraper that is too hard, it can reduce damage to the screen printing screen, thereby extending the service life of the scraper itself and reducing production costs while ensuring printing quality.

[0042] In another embodiment, the scraper is made of polyurethane. Since polyurethane has excellent elasticity and flexibility, the scraper can better fit the shape of the screen and the surface of the circuit board when it contacts the screen and the printed circuit board. Even if there are slight unevenness on the surface of the circuit board or the screen has a certain elastic deformation, the scraper can ensure uniform scraping of the ink through its own elastic adjustment, reducing defects such as missing printing and false printing. In addition, the polyurethane scraper has good chemical stability and can resist the erosion of various chemical substances in the screen printing ink. In the process of long-term contact with the ink, it will not dissolve, swell or deteriorate due to the solvents, additives and other components in the ink, thereby ensuring the stability of the performance of the scraper and thus ensuring the consistency of the printing quality.

[0043] In another embodiment, the length of the scraper is 2.5-4.3 cm longer than the width of the pattern of the screen printing screen on each side.

[0044] Step 4', placing the printed printed circuit board into a drying device, adjusting the temperature of the drying device to 70-90 degrees Celsius for baking for 80-100 minutes.

[0045] The present invention is further described in detail below through specific preferred embodiments, but the present invention is not limited to the following embodiments. Example 1

[0046] A method for preparing a printed circuit board surface protective screen printing ink is specifically implemented according to the following steps: dissolving 5wt% TBT into an anhydrous ethanol solution to obtain solution 1, preparing a 0.5wt% CNF aqueous solution, adding 0.4wt% SDBS thereto to improve the dispersibility of CNF, and then ultrasonically dispersing to obtain solution 2, then adding solution 2 dropwise into an anhydrous ethanol solution 1 containing TBT, and mixing evenly by magnetic stirring at room temperature to obtain solution 3, and finally transferring solution 3 to a reactor for hydrothermal reaction for 10h-12h, and then washing by centrifugation with deionized water and anhydrous ethanol for 4-5 times, and drying the obtained solid in a vacuum oven for 10h-12h to obtain TiO2-CNF modified inorganic pigment nanoparticles. 10 wt% PDMS and 1 wt% curing agent were added to n-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

[0047] A method for preparing a printed circuit board surface protective screen printing ink is specifically implemented according to the following steps: dissolving 5wt% TBT into an anhydrous ethanol solution to obtain solution 1, preparing a 0.5wt% CNF aqueous solution, adding 0.4wt% SDBS thereto to improve the dispersibility of CNF, and then ultrasonically dispersing to obtain solution 2, then adding solution 2 dropwise into an anhydrous ethanol solution 1 containing TBT, and mixing evenly by magnetic stirring at room temperature to obtain solution 3, and finally transferring solution 3 to a reactor for hydrothermal reaction for 10h-12h, and then washing by centrifugation with deionized water and anhydrous ethanol for 4-5 times, and drying the obtained solid in a vacuum oven for 10h-12h to obtain TiO2-CNF modified inorganic pigment nanoparticles. 10 wt % PDMS and 1 wt % curing agent were added to n-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

[0048] A method for preparing a printed circuit board surface protective screen printing ink is specifically implemented according to the following steps: dissolving 5wt% TBT into an anhydrous ethanol solution to obtain solution 1, preparing a 0.5wt% CNF aqueous solution, adding 0.4wt% SDBS thereto to improve the dispersibility of CNF, and then ultrasonically dispersing to obtain solution 2, then adding solution 2 dropwise into an anhydrous ethanol solution 1 containing TBT, and mixing evenly by magnetic stirring at room temperature to obtain solution 3, and finally transferring solution 3 to a reactor for hydrothermal reaction for 10h-12h, and then washing by centrifugation with deionized water and anhydrous ethanol for 4-5 times, and drying the obtained solid in a vacuum oven for 10h-12h to obtain TiO2 / CNF modified inorganic pigment nanoparticles. 10 wt% PDMS and 1 wt% curing agent were added to n-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

[0049] A method for preparing a printed circuit board surface protective screen printing ink is specifically implemented according to the following steps: dissolving 5wt% TBT into an anhydrous ethanol solution to obtain solution 1, preparing a 0.5wt% CNF aqueous solution, adding 0.4wt% SDBS thereto to improve the dispersibility of CNF, and then ultrasonically dispersing to obtain solution 2, then adding solution 2 dropwise into an anhydrous ethanol solution 1 containing TBT, and mixing evenly by magnetic stirring at room temperature to obtain solution 3, and finally transferring solution 3 to a reactor for hydrothermal reaction for 10h-12h, and then washing by centrifugation with deionized water and anhydrous ethanol for 4-5 times, and drying the obtained solid in a vacuum oven for 10h-12h to obtain TiO2 / CNF modified inorganic pigment nanoparticles. 10 wt% PDMS and 1 wt% curing agent were added to n-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

[0050] A method for preparing a printed circuit board surface protective screen printing ink is specifically implemented according to the following steps: dissolving 5wt% TBT into an anhydrous ethanol solution to obtain solution 1, preparing a 0.5wt% CNF aqueous solution, adding 0.4wt% SDBS thereto to improve the dispersibility of CNF, and then ultrasonically dispersing to obtain solution 2, then adding solution 2 dropwise into an anhydrous ethanol solution 1 containing TBT, and mixing evenly by magnetic stirring at room temperature to obtain solution 3, and finally transferring solution 3 to a reactor for hydrothermal reaction for 10h-12h, and then washing by centrifugation with deionized water and anhydrous ethanol for 4-5 times, and drying the obtained solid in a vacuum oven for 10-12h to obtain TiO2 / CNF modified inorganic pigment nanoparticles. 10 wt% PDMS and 1 wt% curing agent were added to n-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

[0051] A method for preparing a printed circuit board using the screen printing ink as described above is specifically implemented according to the following steps: Step 1: Use nylon screen as mesh cloth and prepare a screen printing plate consistent with the surface protection area of ​​the printed circuit board according to the screen printing plate manufacturing method of the prior art.

[0052] Step 2: After the silk screen printing screen is made, the next step is to adjust the alignment, that is, adjust the relative position of the silk screen printing screen and the flexible printed circuit board so that the pattern of the silk screen printing screen is directly opposite to the surface protection area of ​​the flexible printed circuit board to ensure that the liquid ink is printed and coated on the surface protection area of ​​the flexible printed circuit board without coating other areas.

[0053] Step 3, apply the ink prepared in Examples 1-5 on a 220-300 mesh homemade screen printing plate, and manually scrape the TiO2-CNF-PDMS ink with a polyurethane right-angle scraper to evenly apply the liquid TiO2-CNF-PDMS ink to the surface protection area of ​​the flexible printed circuit board. The right-angle scraper has a hardness of 65HA-70HA, the scraper is made of polyurethane, and the length of the scraper is 2.5-4.3 cm longer than the width of the pattern of the screen printing plate on each side.

[0054] Step 4: Place the printed printed circuit board into a drying device, adjust the temperature of the drying device to 70-90 degrees Celsius and bake for 80-100 minutes.

[0055] The performance of the liquid TiO2-CNF-PDMS ink prepared in Examples 1-5 of the present invention was tested after being printed on the surface of a printed circuit board by screen printing, and the results are shown in Tables 1 and 2; Table 1 Comparison of sample surface hydrophobicity test results

[0056] Table 2 Comparison of test results of sample surface UV resistance

[0057] Liquid ink is prepared and printed on the surface of the printed circuit board by screen printing. The hydrophobicity is tested. As can be seen from the above comparison table 1, when a small amount of modified inorganic pigment nanoparticles is added, the hydrophobic angle shows an increasing trend until it is increased to 159 ° to reach a super-hydrophobic effect. With the further increase of the amount of nanoparticles added, agglomeration may occur in the nanoparticles, and the hydrophobic angle is reduced, but it is still in a super-hydrophobic state. Therefore, it can be known that the printed circuit board surface protection screen printing ink prepared by the present invention can make its surface reach a super-hydrophobic effect, and its surface also has good self-cleaning ability.

[0058] The test results of the anti-ultraviolet performance of the surface of the prepared liquid ink after being printed on the surface of the printed circuit board by screen printing can be seen from the following comparison table 2. Under the appropriate addition amount, the nanoparticles are stably fixed on the surface of the flexible printed circuit board to form a stable microstructure, which is conducive to improving the ultraviolet absorption capacity of the surface of the printed circuit board, so the absorbance increases in the 200nm-380nm band. However, when the amount of nanoparticles added is too much, the original microstructure of the surface of the printed circuit board may be destroyed, the propagation path of the light is increased, thereby reducing the absorption and shielding effect of ultraviolet rays, and the absorbance is slightly reduced. Therefore, it can be seen that the printed circuit board surface protection screen printing ink prepared by the present invention has good anti-ultraviolet ability and meets the performance requirements of the flexible printed circuit board when used outdoors.

[0059] In the present invention, TiO2 nanoparticles can absorb ultraviolet light in sunlight, so that the ink has excellent anti-ultraviolet light ability; PDMS has low surface energy and chemical stability, can provide good waterproof performance to the PCB surface, prevent water penetration, and at the same time it has a certain air permeability, allowing gas molecules to pass; under normal conditions, it is not easy to react with other substances, which plays a good antioxidant protection role on the PCB surface. PDMS can also improve the adhesion between the coating surface and the circuit board. Compared with ordinary covering films, the adhesive layer is omitted, saving time, materials and economic costs. The cured TiO2 / CNF / PDMS film layer has flexibility and lubricity, making the PCB surface neat and smooth, avoiding quality problems such as bubbles, poor creases, and uneven thickness generated during the production process of ordinary covering films. CNF has excellent mechanical strength and conductive properties. Using it as a reinforcing material to prepare TiO2 / CNF / PDMS ink can significantly improve the strength and wear resistance of the printed circuit board surface, while also ensuring the realization of the normal conductive transmission function of the printed circuit board.

[0060] As described above, the present invention proposes a method for preparing a surface protective screen printing ink for a printed circuit board, which comprises: step 1, dissolving tetrabutyl titanate (TBT) in an anhydrous ethanol solution to obtain a first solution; step 2, preparing a carbon nanofiber (CNF) aqueous solution, adding a surfactant sodium dodecylbenzene sulfonate (SDBS) thereto, and then ultrasonically dispersing to obtain a second solution; step 3, adding the second solution dropwise to the anhydrous ethanol first solution containing tetrabutyl titanate, and mixing uniformly by magnetic stirring at room temperature to obtain a third solution; step 4, transferring the third solution to a reaction mixture; After 10h-12h of hydrothermal reaction in the kettle, centrifuge and wash with deionized water and anhydrous ethanol for 4-5 times, dry the obtained solid to obtain TiO2-CNF modified inorganic pigment nanoparticles; step 5, add polydimethylsiloxane (PDMS) and an appropriate amount of curing agent to the n-hexane solution and react at room temperature for 1h 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 ultrasonically disperse for 20-40min to obtain the final liquid TiO2-CNF-PDMS ink. Printing the prepared screen printing ink on the surface of the printed circuit board by screen printing can make the surface of the printed circuit board have waterproof, self-cleaning and UV resistance functions, thereby broadening the application scenarios of the printed circuit board.

[0061] It should be emphasized that the embodiments described in the present invention are illustrative rather than restrictive, and therefore the present invention is not limited to the embodiments described in the specific implementation manners, and any other implementation manners derived by those skilled in the art based on the technical solutions of the present invention also fall within the scope of protection of the present invention.

Claims

1. A method for preparing a printed circuit board surface protective screen printing ink, characterized in that: include: Step 1, dissolving tetrabutyl titanate in an anhydrous ethanol solution to obtain a first solution; Step 2, preparing a carbon nanofiber aqueous solution, adding a surfactant, sodium dodecylbenzene sulfonate, to the carbon nanofiber aqueous solution, and then ultrasonically dispersing to obtain a second solution; Step 3, adding the second solution dropwise into the first solution and mixing by magnetic stirring at room temperature to obtain a third solution; Step 4, transferring the third solution to a reactor for hydrothermal reaction for 10h-12h, washing the solution by centrifugation with deionized water and anhydrous ethanol for 4-5 times, and drying the obtained solid to obtain TiO2-CNF modified inorganic pigment nanoparticles; Step 5, adding polydimethylsiloxane and an appropriate amount of curing agent to the n-hexane solution and reacting at room temperature for 1 hour under magnetic stirring to obtain a fourth solution; Step 6, adding a certain amount of TiO2-CNF modified inorganic pigment nanoparticles to the fourth solution, and performing ultrasonic dispersion 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 is 6wt%-10wt%.

2. The preparation method according to claim 1, characterized in that: The mass fraction of tetrabutyl titanate added in step 1 is 5wt%.

3. The preparation method according to claim 2, characterized in that: The mass fraction of the carbon nanofiber aqueous solution in step 2 is: 0.2wt%; the mass ratio of sodium dodecylbenzene sulfonate to carbon nanofiber is 4:5; the ultrasonic power is 120W-150W, and the ultrasonic time is 20min-40min.

4. The preparation method 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 preparation method according to claim 4, characterized in that: The mass fraction of the polydimethylsiloxane added in step 5 is 9%, and the mass ratio of n-hexane, polydimethylsiloxane and curing agent is 100:10:

1.

6. The preparation method according to claim 5, characterized in that: The ultrasonic power during ultrasonic dispersion in step 6 is 120W-150W.

7. A method for preparing a printed circuit board using the screen printing ink according to any one of claims 1 to 6, characterized in that: include: Step 1', making a screen printing screen; Step 2', alignment adjustment, so that the pattern of the screen printing plate is aligned with the surface protection area of ​​the flexible printed circuit board; Step 3', printing the liquid TiO2-CNF-PDMS ink prepared by any one of claims 1 to 6 uniformly onto the surface protection area of ​​the flexible printed circuit board through the pores of the silk screen; Step 4', placing the printed printed circuit board into a drying device, adjusting the temperature of the drying device to 70-90 degrees Celsius for baking for 80-100 minutes.

8. The method according to claim 7, characterized in that In the step 1', the screen printing screen is prepared by using a nylon screen as the mesh.

9. The method according to claim 8, characterized in that The alignment adjustment in step 2' makes the pattern of the silk screen directly opposite to the surface protection area of ​​the flexible printed circuit board, which specifically includes: after the silk screen is made, the alignment adjustment is performed, that is, the relative position of the silk screen and the flexible printed circuit board is adjusted, so that the pattern of the silk screen is directly opposite to 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 without being coated on other areas.

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