Repairable protective coating for surface of circuit board as well as preparation method and use method of repairable protective coating

Abstract

The invention discloses a repairable protective coating for a circuit board surface. The repairable protective coating is prepared from low-viscosity hyperbranched thermoplastic acrylic resin, fluorescent powder, a solvent 1, a flatting agent and a defoaming agent, and the low-viscosity hyperbranched thermoplastic acrylic resin is prepared from a hyperbranched vinyl prepolymer, a monomer, a dispersing agent, an initiator, a chain transfer agent and a solvent 2. The hyperbranched vinyl prepolymer is prepared from a polyhydroxy compound, a bifunctional NCO monomer, a hydroxy acrylic monomer, a polymerization inhibitor and a solvent 3. Self-made hyperbranched thermoplastic acrylic resin is used as a film forming substance of the circuit board surface repairable protective coating, and a proper amount of solvent and assistant are added; the prepared circuit board protective coating has excellent'three-proofing 'performance, mechanical properties such as impact resistance and flexibility, high and low temperature impact resistance, insulating property and dielectric property and the like, and also has the characteristics of reworking and easy removal.

Description

Technical Field

[0001] The present invention belongs to the technical field of coatings for circuit boards, and in particular relates to a reworkable protective coating for the surface of a circuit board, and a preparation method and a use method thereof. Background Art

[0002] Circuit board protective coatings are specially formulated to protect circuit boards and related equipment from environmental damage, thereby increasing and extending their service life and ensuring safety and reliability. Under real-world conditions, such as chemical environments (fuels, coolants, etc.), vibration, high dust levels, salt spray, humidity, and high temperatures, circuit boards can corrode, soften, deform, and mildew, leading to circuit board failures. Circuit board protective coatings are applied to the surface of the circuit board, forming a light and flexible film approximately 25-80μm thick. They protect the circuit board from damage under these harsh conditions. Circuit board protective coatings are categorized by their base material into acrylic, polyurethane, silicone, epoxy, and polyxylene types. To meet specific construction and application requirements, some circuit boards must be reworked and reused. For these circuit boards, thermoplastic acrylic protective coatings must be used to ensure reworkability.

[0003] Acrylic-based circuit board protective coatings primarily utilize high-molecular-weight thermoplastic acrylic resins. Currently, the vast majority are imported, with only a small portion utilizing domestically produced resins. However, domestically produced resins present two major challenges. First, when the molecular weight of a domestic resin is comparable to that of an imported product, the viscosity is significantly higher, resulting in stringing during spraying and severely impacting application quality and efficiency. Second, the molecular weight distribution of domestically produced resins is broad, with a high concentration of small molecules, making them unsuitable for applications requiring high vacuum outflow rates. Summary of the Invention

[0004] The present invention aims to provide a reworkable protective coating for circuit board surfaces, and its production and application methods. Using a self-produced, low-viscosity, hyperbranched, high-molecular-weight thermoplastic acrylic resin as the film-forming substance, this coating addresses the problems of low solids content, thin single-coat thickness, and spray-on stringing caused by the high viscosity of the resin. The coating improves its reworkability, application performance, and temperature resistance.

[0005] The present invention provides a technical solution for a reworkable protective coating for the surface of a circuit board.

[0006]

[0007]

[0008] Further, the leveling agent is one or more of BYK-300, BYK-306, BYK-307, BYK-310, BYK-323, BYK-331, BYK-333, BYK-346, BYK-348, BYK-354, BYK-358N, BYK-361N, BYK-370, BYK-371; the defoaming agent is BYK-141, BYK One or more of BYK-077, BYK-066N, BYK-065, BYK-088, BYK-037, BYK-024, BYK-021, BYK-019, BYK-018, and BYK-017; the phosphor is one of commercially available inorganic phosphors or organic phosphors; and the solvent 1 is one or more of butanone, toluene, xylene, trifluorotoluene, butyl acetate, and cyclohexanone.

[0009] Furthermore, the low-viscosity hyperbranched thermoplastic acrylic resin is composed of the following components in percentage by mass:

[0010]

[0011] The monomer is one or more of n-butyl acrylate, isobutyl acrylate, butyl methacrylate, isobutyl methacrylate, methyl methacrylate, isobornyl methacrylate, and caprolactone acrylate.

[0012] Furthermore, the dispersant is one or more of sodium hydroxide, magnesium chloride, magnesium carbonate, calcium carbonate, barium sulfate, calcium sulfate, calcium phosphate, talc, and kaolin.

[0013] Furthermore, the initiator is one of azobisisobutyronitrile, tert-butyl perbenzoate, dibenzoyl peroxide, lauroyl peroxide, and dimethyl azobisisobutyrate.

[0014] Furthermore, the chain transfer agent is one or more of dodecyl mercaptan, 2-methylhexyl 3-mercaptoacetate, aliphatic mercaptan, trichloroethylene, tetrachloromethane and 2,4-diphenyl-4-methyl-1-pentene.

[0015] Furthermore, the solvent 2 is deionized water.

[0016] Further, the hyperbranched vinyl prepolymer is composed of the following components in percentage by mass:

[0017]

[0018]

[0019] Furthermore, the polyol is one or more of polycarbonate polyol, polyester polyol, polyether polyol, polycaprolactone polyol, pentaerythritol, trimethylolpropane, glycerol, dipropylene glycol, and trimerol; the difunctional NCO monomer is one or more of IPDI, HDI, HMDI, MDI, TDI, etc.; the acrylic acid monomer is one or more of hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, and hydroxypropyl methacrylate; the polymerization inhibitor is one or more of benzoquinone, tetrachlorobenzoquinone, hydroquinone, 4-tert-butylquinone, 2,6-di-tert-butyl-4-methylphenol, diphenylamine, p-phenylenediamine, phenothiazine, ferric chloride, sodium sulfate, and sodium sulfide; and the solvent 3 is one or more of xylene, toluene, butyl acetate, cyclohexane, and amyl acetate.

[0020] In a second aspect, the present application provides a process for preparing a reworkable protective coating for a circuit board surface, which adopts the following technical solution:

[0021] Step 1, preparation of hyperbranched vinyl prepolymer: overlay reflux dehydration synthesis device, first add all the solvent in the formula amount into a three-necked flask, start stirring, and control the stirring speed at 200-400r / min; add the polyhydroxy compound in the formula amount into the three-necked flask, heat to reflux, dehydrate for 1 hour, and then cool to room temperature, then slowly add the difunctional NCO monomer in the formula amount into the three-necked flask and stir for 30 minutes, heat to (50-60) ° C and keep warm for 1 hour, then heat to (80-85) ° C and keep warm for 3 hours, detect N When the CO content reaches the designed value of 2.5%-5.5%, first add the formulated amount of polymerization inhibitor, and then slowly add the hydroxy acrylic acid monomer using a peristaltic pump; keep the reaction at (80-85) ° C for 3 hours. When the NCO content is detected to be less than 0.3%, stop heating and connect the distillation device. After the device is connected, first turn on the vacuum pump and control the vacuum degree to 0.06 MPa. Then start heating and distillation until there are no droplets at the tail pipe of the condenser and the system temperature rises rapidly. Then stop heating and vacuuming, cool the material, discharge it and set aside;

[0022] Step 2, preparation of low-viscosity hyperbranched thermoplastic acrylic resin: first add all the solvent 2 of the formula amount into a three-necked flask, start stirring, control the stirring speed at 200-400r / min, and start to slowly heat up. When the temperature reaches 60-65°C, slowly add the mixed solution of the hyperbranched vinyl prepolymer prepared in step (1) and the monomer, and keep it warm at 60-65°C for 30min; then, add all the dispersant and chain transfer agent, and keep it warm at 60-65°C for 30-60min; after the insulation is completed, slowly heat the temperature to 80°C and add the initiator. The resin particles are heated to 80-85°C for 3 hours, then heated to 90°C and heated to 90-95°C for another 3 hours. After heating, the mixture is cooled to below 35°C and filtered through an 80-mesh sieve to obtain uniform, spherical resin particles. Finally, a sufficient amount of a 5% dilute sulfuric acid aqueous solution is prepared in a beaker using deionized water and concentrated sulfuric acid. The solution is added to the beaker containing the resin particles and stirred with a glass rod for washing. This process is repeated until the conductivity of the washing solution is substantially the same as that of the deionized water used.

[0023] Step 3: Add solvent 1 to the drawing cylinder, and slowly add the low-viscosity hyperbranched thermoplastic acrylic resin prepared in step (2) under high-speed stirring (speed ≥ 1000r / min). After it is completely dissolved, add phosphor, leveling agent and defoaming agent respectively under high-speed stirring (speed ≥ 1000r / min), continue high-speed stirring (speed ≥ 1000r / min) for 20 minutes, and then filter and package to obtain a reworkable protective coating for the surface of the circuit board.

[0024] In the third aspect, the present application provides a method for using a reworkable protective coating for the surface of a circuit board, which can be applied by spraying, dipping, or brushing. When spraying, it is necessary to dilute it with a special diluent for spraying to a viscosity of 50 to 80 mPa.s, the spraying pressure is 0.3 to 0.4 MPa, the distance between the spray gun and the board surface is 20 to 30 cm, and the coating thickness is (20-35) μm. When dipping, it is necessary to dilute it with a special diluent for dipping to a viscosity of 100 to 200 mPa.s, and then vertically immerse the circuit board in the protective coating on the surface of the circuit board. When there are no bubbles in the paint, slowly lift the circuit board out of the paint at a constant speed of 1 to 2 seconds / mm to ensure that the coating evenly covers the surface of the circuit board. After lifting it out, suspend the circuit board above the paint can or dripping tray to allow the paint to drip naturally until most of the excess paint is off the surface. Then place it in an air circulation drying cabinet to dry. When brushing, first stir the paint evenly, then let it stand until there are no bubbles in the paint. Then you can use an art brush to brush it. After brushing, place the circuit board in an air circulation drying cabinet to dry.

[0025] Beneficial effects

[0026] The low-viscosity hyperbranched thermoplastic acrylic resin prepared by the invention has a molecular weight of ≥100,000 and a dissolution viscosity of 198 mPa.s when the non-volatile content is 35%, which greatly reduces the dissolution viscosity of high-molecular-weight thermoplastic acrylic resin.

[0027] Self-made hyperbranched thermoplastic acrylic resin is used as the film-forming material of the reworkable protective coating on the circuit board surface. By adding appropriate amounts of solvents and additives, the prepared circuit board protective coating has excellent "three-proof" performance, impact resistance, flexibility and other mechanical properties, high and low temperature impact resistance, insulation performance and dielectric properties, and is also reworkable and easy to remove. DETAILED DESCRIPTION

[0028] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other implementation methods obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0029] Example 1:

[0030] Hyperbranched vinyl prepolymer synthesis formula:

[0031] Raw material name Addition amount (g) Polycaprolactone polyol CAPA3050 27.9 IPDI 24.8 Hydroxyethyl acrylate 5.5 hydroquinone 0.55 Xylene:Butyl acetate=1:1 41.3

[0032] Hyperbranched vinyl prepolymer synthesis process:

[0033] Connect the reflux dehydration synthesis device, first add all the formulated amount of xylene and butyl acetate into the three-necked flask, start stirring, and control the stirring speed at 200-400r / min; add the formulated amount of polycaprolactone polyol CAPA3050 into the three-necked flask, heat to reflux, dehydrate for 1 hour, then cool to room temperature, then slowly add the formulated amount of IPDI into the three-necked flask and stir for 30 minutes, heat to (50-60)℃ and keep warm for 1 hour, then heat to (80-85)℃ and keep warm for 3 hours, and detect NCO When the content reaches 3.5%, hydroquinone is added first, and then hydroxyethyl acrylate is slowly added using a peristaltic pump; the reaction is kept warm at (80-85)°C for 3 hours. When the NCO content is detected to be less than 1.5%, heating is stopped and the distillation device is overlapped. After the device is overlapped, the vacuum pump is first turned on and the vacuum degree is controlled to 0.06MPa. Then, heating is started for distillation until there are no droplets at the tail pipe of the condenser and the system temperature rises rapidly. Then, heating and vacuuming are stopped, and the material is cooled and discharged for standby use to obtain hyperbranched vinyl prepolymer A.

[0034] Low viscosity hyperbranched acrylic resin synthesis formula:

[0035]

[0036]

[0037] Synthesis process of low viscosity hyperbranched thermoplastic acrylic resin:

[0038] First, add all the formulated amount of deionized water to a three-necked flask, start stirring at a speed of 200-400 rpm, and slowly increase the temperature. When the temperature reaches 60-65°C, slowly add the mixture of hyperbranched vinyl prepolymer A and butyl methacrylate, and incubate at 60-65°C for 30 minutes. Then, add all the sodium hydroxide and tetrachloromethane, and incubate at 60-65°C for 30-60 minutes. After incubation, slowly increase the temperature to 80°C, add dibenzoyl peroxide, and incubate at 80-85°C for 3 hours. Then, increase the temperature to 90°C and continue incubating at 90-95°C for 3 hours. After incubation, stop heating, cool naturally to below 35°C, and filter the material through an 80-mesh sieve to obtain uniform, spherical resin particles. Finally, a sufficient amount of 5% dilute sulfuric acid aqueous solution was prepared in a beaker using deionized water and concentrated sulfuric acid. This solution was added to the beaker containing the resin particles and stirred with a glass rod to wash the particles. This process was repeated until the conductivity of the washing solution was approximately the same as that of the deionized water used. This resulted in a low-viscosity hyperbranched thermoplastic acrylic resin A.

[0039] Circuit board protective coating formula:

[0040] Raw material name Addition amount (g) Low viscosity hyperbranched thermoplastic acrylic resin A 35.0 phosphor 0.2 Xylene: Butanone = 1:1 65.0 BYK 306 0.3 BYK 066N 0.2

[0041] Xylene and butanone are added to a drawing cylinder, and the low-viscosity hyperbranched thermoplastic acrylic resin A prepared in step (2) is slowly added under high-speed stirring (speed ≥ 1000 r / min). After the resin is completely dissolved, phosphor, BYK 306 and BYK 066N are added under high-speed stirring (speed ≥ 1000 r / min). The mixture is stirred at high speed (speed ≥ 1000 r / min) for 20 minutes, and then filtered and packaged to obtain a reworkable protective coating A for the surface of a circuit board.

[0042] Circuit board protective coating process:

[0043] Dilute the coating with a special diluent to a viscosity of 100-200 mPa.s. Then vertically immerse the circuit board in the surface protective coating for 20-25 seconds. When there are no bubbles in the coating, slowly remove the circuit board from the coating at a constant speed of 1-2 seconds / mm to ensure that the coating evenly covers the circuit board surface. After removal, suspend the circuit board over the coating can or dripping tray to allow the coating to drip naturally. After most of the excess coating has fallen off the surface, place it in an air-circulating drying cabinet to dry.

[0044] The main properties of the reworkable protective coating used on the circuit board surface:

[0045] project performance Testing standards Dielectric constant, 1MHz 2.44 GB / T 1409 Insulation resistance, Ω <![CDATA[3.0×10 12 ]]> SJ20671 Suspension viscosity (non-volatile matter content 35%), mPa.s 186 GB / T 9269 Impact, 50cm No cracking or peeling of the paint film GB / T 1732 Flexible, mm 1 GB / T 1731 Adhesion, cross-hatch method Level 1 GB / T 9286 High and low temperature shock (-60℃-120℃, 50 cycles) No cracking or peeling of the paint film GJB 150.5A

[0046] Example 2

[0047] Hyperbranched vinyl prepolymer synthesis formula:

[0048] Raw material name Addition amount (g) Polyether 210 30.0 IPDI 13.2 Hydroxyethyl acrylate 5.5 hydroquinone 0.55 Xylene:Butyl acetate=1:1 51.0

[0049] Hyperbranched vinyl prepolymer synthesis process:

[0050] A reflux dehydration synthesis unit is connected. First, add all the formulated amounts of xylene and butyl acetate to a three-necked flask and start stirring at a speed of 200-400 r / min. Then, add the formulated amount of polyether 210 to the three-necked flask, heat to reflux, dehydrate for 1 hour, and then cool to room temperature. Then, slowly add the formulated amount of IPDI to the three-necked flask and stir for 30 minutes. The temperature is raised to (50-60)°C and held for 1 hour, then raised to (80-85)°C and held for 3 hours. When the NCO content reaches 2.9%, the formulated amount of hydroquinone is first added, followed by the slow addition of hydroxyethyl acrylate using a peristaltic pump. The reaction is maintained at (80-85)°C for 3 hours. When the NCO content is less than 1.0%, heating is stopped and a distillation unit is connected. After the device is connected, first turn on the vacuum pump and control the vacuum degree to 0.06MPa, then start heating and distillation until there are no droplets at the tail pipe of the condenser and the system temperature rises rapidly, stop heating and vacuuming, cool down and discharge the material for standby use, and obtain hyperbranched vinyl prepolymer B.

[0051] Low viscosity hyperbranched acrylic resin synthesis formula:

[0052] Raw material name Addition amount (g) Hyperbranched vinyl prepolymer B 6.5 Isobutyl methacrylate 24.0 Sodium hydroxide 2.25 magnesium chloride 3.25 Benzoyl peroxide 2.0 Dodecyl mercaptan 1.85 Deionized water 60.0

[0053] Synthesis process of low viscosity hyperbranched thermoplastic acrylic resin:

[0054] First, add all the formulated amount of deionized water to a three-necked flask, start stirring at a speed of 200-400 r / min, and slowly increase the temperature. When the temperature reaches 60-65°C, slowly add a mixture of hyperbranched vinyl prepolymer B and isobutyl methacrylate, and incubate at 60-65°C for 30 minutes. Then, add all the sodium hydroxide, magnesium chloride, and dodecyl mercaptan, and incubate at 60-65°C for 30-60 minutes. After incubation, slowly increase the temperature to 80°C, add dibenzoyl peroxide, and incubate at 80-85°C for 3 hours. Then, increase the temperature to 90°C and continue incubating at 90-95°C for another 3 hours. After incubation, stop heating, cool naturally to below 35°C, and filter the material through an 80-mesh sieve to obtain uniform, spherical resin particles. Finally, a sufficient amount of 5% dilute sulfuric acid aqueous solution was prepared in a beaker using deionized water and concentrated sulfuric acid. This solution was added to the beaker containing the resin particles and stirred with a glass rod for washing. This process was repeated until the conductivity of the washing solution was approximately the same as that of the deionized water used. This resulted in a low-viscosity hyperbranched thermoplastic acrylic resin B.

[0055] Circuit board protective coating formula:

[0056]

[0057]

[0058] Add xylene and butanone into a drawing cylinder, and slowly add the low-viscosity hyperbranched thermoplastic acrylic resin B prepared in step (2) under high-speed stirring (speed ≥ 1000 r / min). After the resin is completely dissolved, add phosphor, BYK 306 and BYK 066N respectively under high-speed stirring (speed ≥ 1000 r / min). Continue high-speed stirring (speed ≥ 1000 r / min) for 20 minutes, then filter and package the mixture to obtain a reworkable protective coating B for the surface of a circuit board.

[0059] Circuit board protective coating process:

[0060] Dilute the coating with a dipping diluent to a viscosity of (100-200) mPa.s. Then, vertically immerse the circuit board in the surface protective coating for (20-25) seconds. When no bubbles remain in the coating, slowly remove the circuit board from the coating at a constant speed of (1-2) seconds / mm to ensure even coverage of the coating. After removal, suspend the circuit board over the coating can or drip tray to allow the coating to drip naturally. Once most of the excess coating has fallen off the surface, place the board in an air-circulating drying cabinet to dry.

[0061] The main performances achieved by this circuit board protective coating are:

[0062] project performance Testing standards Dielectric constant, 1MHz 2.48 GB / T 1409 Insulation resistance, Ω <![CDATA[1.2×10 12 ]]> SJ20671 Suspension viscosity (non-volatile matter content 35%), mPa.s 198 GB / T 9269 Impact, 50cm No cracking or peeling of the paint film GB / T 1732 Flexible, mm 1 GB / T 1731 Adhesion, cross-hatch method Level 1 GB / T 9286 High and low temperature shock (-60℃-120℃, 50 cycles) No cracking or peeling of the paint film GJB 150.5A

[0063] The present disclosure has been described using the aforementioned embodiments. However, the aforementioned embodiments are merely exemplary embodiments of the present disclosure. It should be noted that the disclosed embodiments do not limit the scope of the present disclosure. On the contrary, modifications and alterations made without departing from the spirit and scope of the present disclosure are within the scope of patent protection of the present disclosure.

Claims

1. A reworkable protective coating for the surface of a circuit board, characterized in that: Calculated by mass percentage, it is composed of the following components:

2. The reworkable protective coating for the surface of a circuit board according to claim 1, characterized in that: The low-viscosity hyperbranched thermoplastic acrylic resin consists of the following components by mass percentage: The monomer is one or more of n-butyl acrylate, isobutyl acrylate, butyl methacrylate, isobutyl methacrylate, methyl methacrylate, isobornyl methacrylate, and caprolactone acrylate.

3. The reworkable protective coating for the surface of a circuit board according to claim 2, characterized in that: The dispersant is one or more of sodium hydroxide, magnesium chloride, magnesium carbonate, calcium carbonate, barium sulfate, calcium sulfate, calcium phosphate, talc, and kaolin; the initiator is one of azobisisobutyronitrile, tert-butyl perbenzoate, dibenzoyl peroxide, lauroyl peroxide, and dimethyl azobisisobutyrate; the chain transfer agent is one or more of dodecyl mercaptan, 3-mercaptoacetic acid-2-methylhexyl ester, aliphatic mercaptan, trichloroethylene, tetrachloromethane, and 2,4-diphenyl-4-methyl-1-pentene; and the solvent 2 is deionized water.

4. The reworkable protective coating for the surface of a circuit board according to claim 2, characterized in that: The hyperbranched vinyl prepolymer consists of the following components in percentage by mass:

5. The reworkable protective coating for the surface of a circuit board according to claim 4, characterized in that: The polyhydroxy compound is one or more of polycarbonate polyol, polyester polyol, polyether polyol, polycaprolactone polyol, pentaerythritol, trimethylolpropane, glycerol, dipropylene glycol, trimerol; the bifunctional NCO monomer is one or more of IPDI, HDI, HMDI, MDI, TDI, etc.; the acrylic monomer is one or more of hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate; the inhibitor is one or more of benzoquinone, tetrachlorobenzoquinone, hydroquinone, p-tert-butylbenzene, 2,6-di-tert-butyl-p-methylphenol, diphenylamine, p-phenylenediamine, phenothiazine, ferric chloride, sodium sulfate, sodium sulfide; the solvent 3 is one or more of xylene, toluene, butyl acetate, cyclohexane, and amyl acetate.

6. The reworkable protective coating for circuit board surface according to claim 1, characterized in that: The leveling agent is one or more of BYK-300, BYK-306, BYK-307, BYK-310, BYK-323, BYK-331, BYK-333, BYK-346, BYK-348, BYK-354, BYK-358N, BYK-361N, BYK-370, BYK-371; the defoaming agent is BYK-141, BYK- The phosphor is one or more of BYK-077, BYK-066N, BYK-065, BYK-088, BYK-037, BYK-024, BYK-021, BYK-019, BYK-018, and BYK-017; the phosphor is one of commercially available inorganic phosphors or organic phosphors; the solvent 1 is one or more of butanone, toluene, xylene, trifluorotoluene, butyl acetate, and cyclohexanone.

7. A method for preparing the reworkable protective coating for circuit board surface according to any one of claims 1 to 6, characterized in that: The following steps are involved: (1) Preparation of hyperbranched vinyl prepolymer: A reflux dehydration synthesis device was connected. First, all the solvent 3 in the formula amount was added into a three-necked flask, and stirring was started. The stirring speed was controlled at 200-400 r / min. Then, the polyhydroxy compound in the formula amount was added into the three-necked flask, and the temperature was raised to reflux. After dehydration for 1 hour, the temperature was lowered to room temperature. Then, the difunctional NCO monomer in the formula amount was slowly added into the three-necked flask, and the temperature was raised to (50-60)°C and kept for 1 hour. Then, the temperature was raised to (80-85)°C and kept for 3 hours. The N When the CO content reaches the designed value of 2.5%-5.5%, first add the polymerization inhibitor in the formula amount, and then use a peristaltic pump to slowly add the hydroxy acrylic acid monomer; keep the reaction at (80-85) ° C for 3 hours, and when the NCO content is detected to be less than 0.3%, stop heating and overlap the distillation device. After the device overlap is completed, first turn on the vacuum pump, control the vacuum degree to 0.06MPa, and then start heating for distillation until there are no droplets at the tail pipe of the condenser and the system temperature rises rapidly, stop heating and vacuuming, cool down and discharge the material for standby use; (2) Preparation of low-viscosity hyperbranched thermoplastic acrylic resin: First, add all the solvent 2 in the formula into a three-necked flask, start stirring, control the stirring speed at 200-400 r / min, and slowly increase the temperature. When the temperature reaches 60-65° C., slowly add the mixed solution of the hyperbranched vinyl prepolymer and monomer prepared in step (1), and keep the temperature at 60-65° C. for 30 min; then, add all the dispersant and chain transfer agent, and keep the temperature at 60-65° C. for 30-60 min; after the temperature is kept, slowly increase the temperature to 80° C., add the initiator; The solvent is heated at 80-85°C for 3 hours, then the temperature is raised to 90°C, and the temperature is continued to be heated at 90-95°C for 3 hours; after the insulation is completed, the heating is stopped, the temperature is naturally lowered to below 35°C, and the material is filtered out using an 80-mesh screen to obtain uniform, spherical resin particles; finally, a sufficient amount of 5% dilute sulfuric acid aqueous solution is prepared in a beaker using deionized water and concentrated sulfuric acid, and the solution is added to the beaker containing the resin particles, and the mixture is stirred and washed using a glass rod; this process is repeated until the conductivity of the washing liquid is substantially the same as the conductivity of the deionized water used; (3) Add solvent 1 into the pull cylinder according to the formula amount, slowly add the low-viscosity hyperbranched thermoplastic acrylic resin prepared in step (2) under high-speed stirring (speed ≥ 1000 r / min), and after it is completely dissolved, add phosphor, leveling agent and defoaming agent respectively under high-speed stirring, i.e., speed ≥ 1000 r / min, continue to stir at high speed, i.e., speed ≥ 1000 r / min, filter and package after 20 minutes, and obtain a reworkable protective coating for the surface of a circuit board.

8. A method for using the reworkable protective coating for a circuit board surface according to any one of claims 1 to 6, characterized in that: The following steps are involved: The repairable protective coating on the surface of the circuit board can be applied by spraying, dipping or brushing. When spraying, it is necessary to dilute it with a special diluent for spraying to a viscosity of 50-80mPa.s, the spraying pressure is 0.3-0.4Mpa, and the distance between the spray gun and the board surface is 20-30cm. When dipping, it is necessary to dilute it with a special diluent for dipping to a viscosity of 100-200mPa.s, and then immerse the circuit board vertically in the protective coating on the surface of the circuit board and keep it for 20-25s. When there are no bubbles in the coating, slowly lift the circuit board out of the coating at a uniform speed of 1-2s / mm to ensure that the coating is evenly covered on the surface of the circuit board. After lifting it out, the circuit board should be suspended above the coating can or drip tray to allow the coating to drip naturally until most of the excess coating is off the surface, and then place it in an air circulation drying cabinet for drying. When brushing, first stir the coating evenly, and then let it stand until there are no bubbles in the coating, and then use an art brush for brushing. After brushing, place the circuit board in an air circulation drying cabinet for drying.

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