Super-hydrophobic three-proofing coating material for PCB (Printed Circuit Board) surface as well as preparation method and application thereof

Abstract

The invention relates to a super-hydrophobic three-proofing coating material for a PCB (printed circuit board) surface and a preparation method and application thereof, the three-proofing coating material comprises a primer and a finishing coat, the primer comprises the following raw materials: adhesive resin, an auxiliary agent and a powder dispersion liquid according to a mass ratio of (10-30): (0.3-2): 100; the powder dispersion liquid is prepared by adding nano silicon dioxide, aluminum hydroxide and silane modified diatomite into an organic solvent and uniformly dispersing; the finishing paint is prepared from the following raw materials: silica sol alkalization liquid, organic alcohol and chlorosilane; the ratio of the silica sol to the organic alcohol is (10-15) g: (700-900) mL, and the dosage of the chlorosilane accounts for 4-6% of the total mass of the silica sol alkalization liquid and the organic alcohol. A three-proofing coating formed by the primer and the finish paint has a great static water contact angle and an extremely low rolling angle, so that water drops can quickly slide down after being generated, accumulation of corrosion factors is effectively reduced, and corrosion of corrosion factors such as moisture to a PCB (printed circuit board) is reduced.

Description

Technical Field

[0001] The present invention relates to the field of coating materials, and particularly to a superhydrophobic three-proof coating material for the surface of a PCB board, a preparation method thereof, and an application thereof. Background Art

[0002] The three-proof paint is a special formula coating used to protect the circuit board and its related equipment from environmental erosion. At present, there are mainly six types of three-proof paints widely used: parylene three-proof paint, polyurethane three-proof paint, acrylic resin three-proof paint, epoxy resin three-proof paint, synthetic rubber three-proof paint, and silicone three-proof paint.

[0003] Among them, parylene three-proof paint is mostly formed into a film by plasma spraying, with good protection performance, but the requirements for equipment and raw materials are extremely high; polyurethane three-proof paint has poor yellowing resistance and has problems of aging and sticking in high-temperature and high-humidity environments; the raw materials of acrylic resin three-proof paint are relatively expensive and have poor light aging resistance; epoxy resin three-proof paint has poor flexibility, high shrinkage rate, and difficult rework; synthetic rubber three-proof paint can form a thin film on the surface of the circuit board by solvent volatilization, with good protection performance, but has extremely poor adhesion to the substrate; silicone three-proof paint has excellent electrical protection performance and weather resistance, but is relatively expensive.

[0004] The protection means of these three-proof paints mainly lies in the shielding effect on corrosion factors. However, under long-term humid conditions, after corrosion factors such as moisture accumulate on the surface of the substrate, it is inevitable to penetrate into the coating and cause damage. Summary of the Invention

[0005] The purpose of the present invention is to overcome the above technical deficiencies, provide a superhydrophobic three-proof coating material for the surface of a PCB board, a preparation method thereof, and an application thereof, and solve the technical problem that the shielding effect of the three-proof paint on corrosion factors such as moisture in the prior art is poor.

[0006] To achieve the above technical purpose, the technical solution provided by the present invention is as follows: In the first aspect, the present invention provides a superhydrophobic three-proof coating material for the surface of a PCB board, including a primer and a topcoat. Among them, the raw materials of the primer include an adhesive resin, an auxiliary agent, and a powder dispersion liquid with a mass ratio of (10 - 30):(0.3 - 2):100; the powder dispersion liquid is prepared by uniformly dispersing nano-silica, aluminum hydroxide, and silane-modified diatomite in an organic solvent; the raw materials of the topcoat include a silica sol alkalization solution, an organic alcohol, and a chlorosilane; the silica sol alkalization solution is obtained by alkalizing silica sol; the ratio between the silica sol and the organic alcohol is (10 - 15) g:(700 - 900) mL, and the dosage of the chlorosilane accounts for 4 - 6% of the total mass of the silica sol alkalization solution and the organic alcohol.

[0007] Second aspect, the present invention provides a preparation method of a superhydrophobic three-proof coating material for the surface of a PCB board, comprising the following steps: adding nano-silica, aluminum hydroxide and silane-modified diatomite into an organic solvent and dispersing uniformly to obtain a powder dispersion liquid, mixing an adhesive resin, an auxiliary agent and the powder dispersion liquid uniformly to obtain a primer; alkalizing silica sol to obtain a silica sol alkalization liquid, mixing and dispersing the silica sol alkalization liquid and an organic alcohol uniformly, and then adding chlorosilane, and standing for 20-26 h to obtain a topcoat.

[0008] Third aspect, the present invention provides a construction process of a superhydrophobic three-proof coating for the surface of a PCB board, comprising the following steps: coating a primer on the surface of the PCB board, and coating a topcoat after the surface is dried to obtain a superhydrophobic three-proof coating on the surface of the PCB board.

[0009] Compared with the prior art, the beneficial effects of the present invention include: The nano-silica in the primer of the present invention can be well stored in the silane-modified diatomite to form microspheres with a micro-nano structure, which can be evenly distributed in the adhesive resin and can maintain long-term hydrophobicity after drying into a film. At the same time, the addition of aluminum hydroxide can improve the electrical properties of the coating; adding chlorosilane to the topcoat to form a network with silica sol helps its long-term hydrophobic stability. The three-proof coating formed by this primer and topcoat has a very large static water contact angle (greater than 150°) and a very low rolling angle (less than 10°), which can make water droplets slide off quickly after generation, effectively reduce the accumulation of corrosion factors, and reduce the corrosion of corrosion factors such as moisture on the PCB board. Description of the Drawings

[0010] Figure 1 is a schematic diagram of the action mechanism of the primer of the present invention; Figure 2 is an electron micrograph of the silica sol used in Comparative Example 1 of the present invention; Figure 3 is an electron micrograph of the silica sol used in Example 1 of the present invention. Detailed Embodiments

[0011] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0012] In view of the defect that the current three-proof paint has a poor shielding effect on corrosion factors such as moisture under long-term humid conditions, the present invention provides a super-hydrophobic three-proof coating material for a PCB board surface and a preparation method thereof. The super-hydrophobic three-proof coating material has a very large static water contact angle and an extremely low rolling angle, which can make water droplets slide off quickly after being generated. It can reduce the enrichment of corrosion factors on the surface of the substrate, thereby greatly delaying the corrosion effect of corrosion factors such as moisture on the PCB board, and the coating construction process is simple.

[0013] In a first aspect, the present invention provides a super-hydrophobic triple-conformal coating material for a PCB surface, comprising a primer and a topcoat, wherein: The raw materials of the primer include an adhesive resin, an additive and a powder dispersion in a mass ratio of (10-30): (0.3-2): 100; the powder dispersion is prepared by adding nano silicon dioxide, aluminum hydroxide and silane-modified diatomaceous earth into an organic solvent and uniformly dispersing them; The raw materials of the topcoat include silica sol alkalization liquid, organic alcohol and chlorosilane; the silica sol alkalization liquid is obtained by alkalizing silica sol; the ratio between silica sol and organic alcohol is (10-15) g: (700-900) mL, and the amount of chlorosilane accounts for 4-6% of the total mass of the silica sol alkalization liquid and the organic alcohol.

[0014] Preferably, the adhesive resin includes fluorosilicone resin; the auxiliary agent includes one or more of a dispersant and a leveling agent. The present invention uses fluorosilicone resin to provide excellent weather resistance, that is, in addition to having extremely high hydrophobic properties, the coating of the present invention also has excellent weather resistance such as acid and alkali resistance, temperature change resistance, and artificial weather aging resistance due to the use of fluorosilicone resin as the base material. It has the characteristics of good shielding effect on corrosion factors. At the same time, due to its low surface energy characteristics, it is difficult for corrosion factors to adhere to its surface (anti-fouling), further improving its anti-corrosion ability. At the same time, fluorosilicone resin has the advantages of both fluorocarbon and silicone, and is low in cost.

[0015] Preferably, in the powder dispersion, the mass ratio of the powder to the organic solvent is (5-15):(85-95). The powder includes nano-silicon dioxide, aluminum hydroxide and silane-modified diatomaceous earth.

[0016] Preferably, the mass ratio of nano-silicon dioxide, silane-modified diatomaceous earth and aluminum hydroxide is (5-7): (2-3): 1; more preferably 7:3:1.

[0017] Preferably, the organic solvent includes one or more of xylene and butyl acetate.

[0018] Preferably, the silica sol includes chain silica sol, and more preferably Nissan Chemical MEK-ST-IP type silica sol.

[0019] Preferably, the chlorosilane comprises perfluorodecyltrichlorosilane.

[0020] In a second aspect, the present invention provides a method for preparing a superhydrophobic three-proof coating material for the surface of a PCB board, comprising the following steps: Adding nano-silica, aluminum hydroxide and silane-modified diatomite into an organic solvent and dispersing uniformly to obtain a powder dispersion liquid, and mixing the adhesive resin, the auxiliary agent and the powder dispersion liquid uniformly to obtain a primer; Alkalizing the silica sol to obtain a silica sol alkalization liquid, mixing and dispersing the silica sol alkalization liquid and the organic alcohol uniformly, and then adding chlorosilane, and standing for 20 - 26 h to obtain a topcoat.

[0021] Preferably, nano-silica, aluminum hydroxide and silane-modified diatomite are added into an organic solvent and dispersed uniformly through grinding for 1.5 - 2.5 h.

[0022] Preferably, the preparation steps of the silane-modified diatomite include: dispersing diatomite in an alkaline alcohol solution, adding n-octyltriethoxysilane, and performing a silanization treatment, and drying to obtain the silane-modified diatomite.

[0023] More preferably, the ratio of diatomite to the alkaline alcohol solution is (20 - 40) g : (600 - 1000) mL; the addition amount of n-octyltriethoxysilane is 0.1 - 0.5% of the total mass of diatomite and the alkaline alcohol solution.

[0024] More preferably, the alkaline alcohol solution is prepared by mixing ethanol, deionized water and 28 wt% ammonia water in a volume ratio of 20:2:1.

[0025] More preferably, the silanization treatment is a stirring reaction at 45 - 55 °C for 22 - 26 h; freeze drying is used for drying.

[0026] Preferably, the preparation steps of the silica sol alkalization liquid specifically include: mixing silica sol, deionized water and ammonia water in a ratio of (10 - 15) g : (70 - 90) mL : (30 - 50) mL and stirring for 8 - 12 min to obtain the silica sol alkalization liquid.

[0027] In a third aspect, the present invention provides a construction process for a superhydrophobic three-proof coating on the surface of a PCB board, comprising the following steps: coating a primer on the surface of the PCB board, and coating a topcoat after surface drying to obtain a superhydrophobic three-proof coating on the surface of the PCB board.

[0028] Preferably, surface drying is performed at room temperature for 25 - 35 min after coating the primer on the surface of the PCB board.

[0029] Preferably, the dry film thickness of the primer is 20 - 30 μm, and the total film thickness of the primer and the topcoat is 30 - 40 μm.

[0030] The main action mechanism and advantages of the present invention: (1) Refer to Figure 1 , the nano-silica in the primer of the present invention can be well stored in the pores of silylated diatomite, thereby forming microspheres with a micro-nano structure. The microspheres can be evenly distributed in the resin added subsequently, and long-term hydrophobicity can be maintained after drying into a film; the addition of aluminum hydroxide can improve the electrical properties of the coating, making the material have high electrical strength and volume resistivity.

[0031] (2) By adding perfluorodecyltrichlorosilane to the topcoat in the present invention, self-condensation will occur spontaneously during the functionalization process, which plays a crucial role in the formation of the network. The trichlorosilyl groups on the silane and the hydroxyl groups on the silica mainly form covalent bonds through a condensation reaction, thereby forming a primary functional layer on the surface of the silica nanoparticles. In the presence of sufficient trichlorosilane, the trichlorosilyl groups on the silane form oligomers through random self-condensation reactions. When the trichlorosilane is in excess, the oligomers further react to form a network. Therefore, the superhydrophobic three-proof coating embedding silica nanoparticles has a dense fluoroalkyl network filler in the sub-nanometer and nanometer regions, which contributes to the long-term hydrophobic stability of the three-proof coating.

[0032] The present invention will be further described in detail below through specific examples.

[0033] Example 1 A preparation method of a superhydrophobic three-proof coating material for the surface of a PCB board, comprising the following steps: S1, preparing the primer: S101, preparation of modified diatomite: First, disperse 30 g of diatomite in 1000 mL of a solution containing ethanol, deionized water, and ammonia water (mass fraction 28%) with a volume ratio of 20:2:1 and perform mechanical stirring, then add 4 wt% of n-octyltriethoxysilane, and stir at 50 °C for 24 h to silylate the surface of the diatomite; finally, perform freeze-drying to obtain silylated diatomite powder; S102, preparation of the powder dispersion: Add a mixed powder of 10 g of nano-silica, silylated diatomite, and aluminum hydroxide (mass ratio 7:3:1) with a total mass to 90 g of a solvent (a compound of xylene and butyl acetate in a mass ratio of 3:2), and grind and disperse for 2 h to obtain a powder dispersion; S103, preparation of the primer: Select 20 g of fluorosilicone resin as the bonding resin, add 100 g of the powder dispersion, 0.6 g of Dow Corning DC-3 silicone dispersant, and 0.6 g of Dow Corning 205SL silicone leveling agent, and prepare the primer of the superhydrophobic three-proof coating material for the surface of the PCB board through processes such as stirring and dispersion.

[0034] S2, preparing the topcoat: Select 12 g of Nissan Chemical's MEK-ST-IP type silica sol (chain-like), 80 mL of deionized water, and 40 mL of ammonia water (mass fraction of 28%) for dispersion and alkalization for 10 min to obtain an alkalized silica sol solution, and then add it to 800 mL of absolute ethanol for dispersion for 30 min. Finally, slowly add perfluorodecyltrichlorosilane accounting for 5% of the total mass of the alkalized silica sol solution and absolute ethanol, and let it stand for 24 h to obtain the topcoat of the superhydrophobic three-proof coating material for the PCB board surface.

[0035] It can be applied on the PCB board surface by air spraying. The dry film thickness of the primer is about 20 μm. It can be surface dry after drying at room temperature for 30 min, and then continue to spray the topcoat. The total film thickness is about 30 μm to obtain the superhydrophobic three-proof coating.

[0036] Comparative Example 1 The difference from Example 1 is only that: ordinary silica sol (granular) is used to replace the silica sol (chain-like) in Example 1, and other steps and conditions are the same as those in Example 1.

[0037] The electron micrographs of the silica sols used in Example 1 and Comparative Example 1 are as Figure 2 and Figure 3 shown, Figure 2 is ordinary silica sol, Figure 3 is chain-like silica sol. Compared with ordinary silica sol, chain-like silica sol can form a denser network structure with perfluorodecyltrichlorosilane, thus producing better water immersion resistance.

[0038] The hydrophobic performance of the three-proof coatings obtained in Example 1 and Comparative Example 1 was tested according to GB / T 23764-2009 "Test Method for the Performance of Photocatalytic Self-Cleaning Materials", and the results are shown in Table 1 below.

[0039] Table 1 Test results of the hydrophobic performance of the three-proof coatings obtained in Example 1 and Comparative Example 1

[0040] The test results show that the coating prepared with silica sol (chain-like) in Example 1 is more excellent in liquid immersion resistance than the coating prepared with ordinary silica sol (granular) in Comparative Example 1.

[0041] After soaking the sample board in water for 24 h, the PCB board of Example 1 can still be powered on and operated. Experiments show that this coating can effectively protect the PCB board under humid conditions and significantly improve its service life; while the circuit in the PCB board of Comparative Example 1 is in a short-circuit state, resulting in a break in the signal processing or transmission line and a failure.

[0042] Example 2 The difference from Example 1 is only that the dosages of colloidal silica (chain-like) are adjusted to be 4 g, 10 g, 15 g, and 20 g respectively, and other steps and conditions are the same as those in Example 1.

[0043] The test results show that when the dosage of colloidal silica (chain-like) is excessive, perfluorodecyltrichlorosilane is insufficient, and only a primary functional layer on the nanoparticles can be formed during the functionalization process, resulting in an incompact functional layer structure and weakened durability. When the dosage of colloidal silica (chain-like) is too small, a large amount of excessive perfluorodecyltrichlorosilane undergoes self-condensation and cannot form a network structure with colloidal silica (chain-like). Therefore, the preferred dosage of colloidal silica (chain-like) in the present invention is 10 - 15 g. After testing, the static water contact angle of the obtained coating is greater than 150°, and the rolling angle is less than 10°. Further preferably, the dosage of colloidal silica (chain-like) is 12 g used in Example 1.

[0044] Comparative Example 2 The difference from Example 1 is only that aluminum hydroxide is removed, and other steps and conditions are the same as those in Example 1.

[0045] The electrical properties of the superhydrophobic three-proof coatings obtained in Example 1 and Comparative Example 2 were tested. Among them, the test standard for electrical strength refers to GB / T 1408.1 - 2016, and the test standard for volume resistivity refers to GB / T 31838.2 - 2019; the results are shown in Table 2 below.

[0046] Table 2 Test results of the electrical properties of the three-proof coatings obtained in Example 1 and Comparative Example 2

[0047] As can be seen from Table 2, the addition of aluminum hydroxide can improve the electrical properties of the coating, and both the electrical strength and volume resistivity of the obtained three-proof coating are improved, indicating better insulation performance.

[0048] The specific embodiments of the present invention described above do not constitute a limitation on the protection scope of the present invention. Any other corresponding changes and deformations made according to the technical concept of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A super hydrophobic three-proof coating material for PCB board surface, characterized in that: Including primer and topcoat, among which, The raw materials of the primer include an adhesive resin, an auxiliary agent and a powder dispersion in a mass ratio of (10-30): (0.3-2): 100; the powder dispersion is prepared by adding nano silicon dioxide, aluminum hydroxide and silane-modified diatomaceous earth into an organic solvent and uniformly dispersing them; The raw materials of the topcoat include silica sol alkalization liquid, organic alcohol and chlorosilane; the silica sol alkalization liquid is obtained by alkalizing silica sol; the ratio between the silica sol and the organic alcohol is (10-15) g: (700-900) mL, and the amount of the chlorosilane accounts for 4-6% of the total mass of the silica sol alkalization liquid and the organic alcohol.

2. The super-hydrophobic triple-proof coating material for PCB board surface according to claim 1, characterized in that: The adhesive resin includes fluorosilicone resin; the auxiliary agent includes one or more of a dispersant and a leveling agent.

3. The super hydrophobic triple-proof coating material for PCB board surface according to claim 1, characterized in that: The mass ratio of powder to organic solvent in the powder dispersion is (5-15): (85-95); The mass ratio of the nano-silicon dioxide, the aluminum hydroxide and the silane-modified diatomaceous earth is 7:1:3; The organic solvent includes one or more of xylene and butyl acetate.

4. The super hydrophobic triple-proof coating material for PCB board surface according to claim 1, characterized in that: The silica sol includes chain silica sol; The chlorosilane includes perfluorodecyltrichlorosilane.

5. The method for preparing a super-hydrophobic triple-proof coating material for a PCB surface as claimed in any one of claims 1 to 4, characterized in that: The following steps are involved: Nano-silicon dioxide, aluminum hydroxide and silane-modified diatomaceous earth are added to an organic solvent and dispersed uniformly to obtain a powder dispersion, and a bonding resin, an auxiliary agent and the powder dispersion are mixed uniformly to obtain a primer; The silica sol is subjected to alkalization treatment to obtain a silica sol alkalization liquid, the silica sol alkalization liquid and organic alcohol are mixed and dispersed uniformly, and then chlorosilane is added and allowed to stand for 20 to 26 hours to obtain a topcoat.

6. The method for preparing the super-hydrophobic triple-proof coating material for PCB board surface according to claim 5, characterized in that: The nano silicon dioxide, aluminum hydroxide and silane-modified diatomaceous earth are added into an organic solvent and are evenly dispersed after grinding for 1.5 to 2.5 hours.

7. The method for preparing the super-hydrophobic triple-proof coating material for PCB board surface according to claim 5, characterized in that: The preparation steps of the silane-modified diatomaceous earth include: dispersing the diatomaceous earth in an alkaline alcohol solution, adding n-octyltriethoxysilane, subjecting the diatomaceous earth to silanization treatment, and drying to obtain the silane-modified diatomaceous earth.

8. The method for preparing the super-hydrophobic triple-proof coating material for PCB board surface according to claim 7, characterized in that: The ratio of the diatomaceous earth to the alkaline alcohol solution is (20-40) g: (600-1000) mL; The amount of n-octyltriethoxysilane added is 0.1-0.5% of the total mass of the diatomaceous earth and the alkaline alcohol solution; The alkaline alcohol solution is prepared by mixing ethanol, deionized water and 28 wt % ammonia water in a volume ratio of 20:2:1; The silanization treatment is carried out by stirring the reaction at 45-55° C. for 22-26 hours; and the drying is carried out by freeze drying.

9. The method for preparing the super-hydrophobic triple-proof coating material for PCB board surface according to claim 5, characterized in that: The preparation steps of the silica sol alkalization liquid specifically include: mixing silica sol, deionized water and ammonia water in a ratio of (10-15) g: (70-90) mL: (30-50) mL, stirring for 8-12 minutes, and obtaining the silica sol alkalization liquid.

10. A construction process for a super-hydrophobic triple-proof coating on a PCB surface, characterized in that: The following steps are involved: A primer is applied on the surface of the PCB board, and a topcoat is applied after the surface is dried to obtain a super-hydrophobic three-conformal coating on the surface of the PCB board; the primer and the topcoat are the primer and the topcoat in the super-hydrophobic three-conformal coating material for the surface of the PCB board as described in any one of claims 1-4.

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