Preparation method of microcapsule type self-adaptive sealant

Abstract

The invention discloses a preparation method of a microcapsule type self-adaptive sealant, which is characterized in that a phase separation process occurs when a low-boiling-point solvent is volatilized due to different hydrophobicity of a capsule wall material and a capsule core material by a solvent evaporation phase separation method, and the capsule wall material with lower hydrophobicity is preferentially migrated to a water-oil interface to form a capsule wall. According to the method, the five procedures of glue preparation, glue mixing, glue dipping, assembling and glue removing of traditional sealing are reduced to be one procedure of pre-coating, and the defects that the airplane sealing process is tedious, and sealing is prone to losing efficacy are effectively overcome.

Description

Technical Field

[0001] The invention belongs to the technical field of corrosion protection and sealing of polymer material products, and in particular relates to a method for preparing a microcapsule-type adaptive sealant. Background Art

[0002] In the design and manufacturing of civil aircraft, due to the limitations of sealing materials and construction processes, the assembly process is complicated and inefficient, and many fasteners on the aircraft are not wet assembled or sealed. For example, there are gaps between the skin and the fasteners at the rivet holes or screw holes. Fatigue vibration during flight causes the paint layer to crack or peel off, and moisture and dirt invade to form a corrosion source, causing corrosion of the fasteners and surrounding skin.

[0003] During the production process, the sealing quality is difficult to ensure, and it is difficult to repair the seals of civil aircraft in time after failure during operation. Liquids containing corrosive media (rainwater, cleaning water, condensation water, etc.) penetrate into the structural connections where gaps exist, causing corrosion of the aircraft connections, which in turn affects the sealing environment in the cabin and causes corrosion of the aircraft system accessories and onboard electronic equipment. Summary of the invention

[0004] Purpose of the Invention

[0005] In view of the problems currently faced by aircraft, such as complex sealing assembly process, low efficiency and difficulty in ensuring assembly quality, the present invention provides a method for preparing a microcapsule-type adaptive sealant.

[0006] Inventing technical solutions

[0007] A method for preparing a microcapsule-type adaptive sealant comprises the following steps:

[0008] Step 1: Select liquid polysulfide rubber as the core material and polystyrene as the wall material, add them to the solvent, and form a completely miscible, uniform and stable oil phase solution by uniform stirring; weigh the emulsifier, add it to deionized water, and prepare an emulsifier solution with a concentration of 2wt% by stirring; then, at a set speed, drop the oil phase solution into the emulsifier solution to form an oil-in-water emulsion;

[0009] Step 2: The formed emulsion system is evaporated at a set speed to remove the solvent; during the solvent evaporation process, the interfacial tension and surface energy drive the hydrophilic wall material to continuously migrate to the interface between the polysulfide rubber and water, and finally form microcapsules with liquid polysulfide rubber wrapped around the core material;

[0010] Step 3: After the solvent is completely evaporated, the remaining solution is subjected to high-speed centrifugation to obtain a precipitate, and the precipitate is fully washed with deionized water and dried to obtain polysulfide rubber microcapsule powder;

[0011] Step 4: Take the microcapsule powder, add plasticizer, tackifier, reinforcing agent, accelerator, curing agent in sequence and stir evenly;

[0012] Step 5: Degas the mixed sealant in a vacuum box.

[0013] Preferably, the mass ratio of the components in the first step is: core material: capsule wall: solvent: emulsifier = 2.5:1: 20-40: 0.6-0.7.

[0014] Preferably, the solvent in the first step is a low boiling point solvent, and the solvent that can be used includes dichloromethane.

[0015] Preferably, the rotation speed is set to 1000 rpm in the first step.

[0016] Preferably, the rotation speed is set to 500 rpm in the second step.

[0017] Preferably, the high-speed centrifugation speed in the third step is 8000 rpm.

[0018] Preferably, in the fourth step, the mass ratio of the microcapsule powder, the plasticizer, the tackifier, the reinforcing agent, the accelerator, and the curing agent is 100:30-40:5-10:2-4:1-3:20-40.

[0019] Preferably, in the fourth step, the plasticizer is dibutyl phthalate, the tackifier is epoxy resin, the reinforcing agent is silicon dioxide or carbon black, the accelerator is diphenylguanidine, and the curing agent is manganese dioxide.

[0020] Preferably, the temperature during the fourth step of mixing is no greater than 35°C.

[0021] Preferably, after the fifth step, the degassed sealant is applied to the surface of the target substrate, and a vulcanization reaction is performed by controlling the ambient temperature and humidity conditions.

[0022] Preferably, when a 90° countersunk bolt is used as the target substrate, the sealant coating thickness is 0.4 mm to 0.5 mm.

[0023] Advantages of the present invention: This method reduces the five processes of traditional sealing, namely, glue preparation, glue mixing, glue dipping, assembly and glue removal, to one process of pre-coating, effectively overcoming the defects of complicated aircraft sealing process and easy failure of sealing. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the structural diagram of a 90° countersunk bolt.

[0025] Figure 2 Schematic diagram of the solvent evaporation process. DETAILED DESCRIPTION

[0026] The present invention is achieved through the following technical solutions.

[0027] The invention discloses a method for preparing a microcapsule type self-adaptive sealant, which adopts a solvent evaporation phase separation method.

[0028] The solvent evaporation phase separation method mainly uses the different hydrophobicity of the capsule wall and the capsule core materials to cause the phase separation process when the low boiling point solvent evaporates. The capsule wall material with lower hydrophobicity preferentially migrates to the water-oil interface to form the capsule wall. The schematic diagram of the evaporation process is shown in Figure 2 shown.

[0029] In the process of preparing microcapsules, temperature, stirring speed, core-to-wall ratio and emulsifier concentration will affect the morphology, size, size distribution and agglomeration of microcapsules. According to the single variable control method, other experimental conditions remain unchanged to optimize the synthesis process of microcapsules.

[0030] The method comprises the following steps:

[0031] Step 1: Select the core material and wall material, add them to a low boiling point solvent, and form a completely miscible, uniform and stable oil phase solution by stirring at a constant speed at 30°C. Weigh the emulsifier, add it to deionized water, and stir to prepare a 2wt% emulsifier solution. Then, at 1000rpm, slowly drop the oil phase solution into the water phase solution containing the emulsifier to form an oil-in-water (O / W) emulsion. The proportions of each component are shown in Table 1.

[0032] Step 2: The formed emulsion system is evaporated at 500 rpm and a constant temperature of 25°C to remove the low-boiling point solvent. During the solvent evaporation process, the interfacial tension and surface energy drive the hydrophilic wall material to continuously migrate to the interface between the polysulfide rubber and water, and finally form microcapsules with liquid polysulfide rubber encapsulating the core material.

[0033] Table 1 Microcapsule preparation materials and ratios

[0034] Components name Model / Abbreviation Quality Ratio core material Liquid polysulfide rubber LP-3 2.5 Cyst wall Polystyrene PS 1 Solvents Dichloromethane DCM 20～40 Emulsifier Sodium Oleate NaOA 0.6～0.7

[0035] Step 3: After the solvent is completely evaporated, the remaining solution is subjected to high-speed centrifugation at 8000 rpm to obtain a precipitate, and the precipitate is fully washed with deionized water for 3 times, and then dried to obtain polysulfide rubber microcapsule powder.

[0036] Table 2 Selection of process parameters

[0037] Experimental conditions Core:wall (mass ratio) Stirring rate Evaporation temperature Emulsifier concentration Process parameters 2.5:1 500r / min 25℃ 2wt%

[0038] Step 4: Compounding process, plasticizer adjustment: If microcapsule powder is taken, add plasticizer (dibutyl phthalate) as the viscosity regulator of the sealant.

[0039] Addition of tackifier: Add epoxy resin tackifier under stirring to ensure that the prepared sealant has good adhesion and construction performance.

[0040] Introduction of reinforcing agent: Add reinforcing agent (such as silica or carbon black) to the mixed liquid and stir it evenly. The addition of reinforcing agent will improve the mechanical strength and durability of the sealant.

[0041] Introduction of accelerator: Add accelerator (diphenylguanidine) to the mixture, ensuring its uniform distribution to accelerate the vulcanization reaction.

[0042] Curing agent mixing: gradually add manganese dioxide curing agent into the microcapsule dispersion and stir evenly. The stirring speed should be moderate to avoid microcapsule rupture and ensure that the curing agent is in full contact with the microcapsule surface.

[0043] The addition amounts of tackifier, reinforcing agent and curing agent are shown in Table 3.

[0044] The temperature during the mixing process was controlled to be no greater than 35°C to avoid excessively high temperatures causing microcapsule rupture or premature reaction of the curing agent.

[0045] Table 3 Mass ratio of each component of sealant

[0046] Matrix Microcapsule powder 100 Plasticizers Dibutyl phthalate 30～40 Tackifying resin Epoxy E51 5～10 Reinforcement filler Fumed Silica 2～4 Accelerator diphenylguanidine 1～3 Curing agent Manganese dioxide 20～40

[0047] Step 5: Control the curing process. Degas the mixed sealant in a vacuum box to remove bubbles introduced during the mixing process and prevent the formation of pores after curing.

[0048] Apply the degassed sealant to the target substrate surface and control the ambient temperature to 0°C.

[0049] -35℃ and humidity condition 40%-80% for vulcanization reaction. Ensure uniformity during curing to obtain uniform curing effect.

[0050] Example

[0051] A method for preparing a microcapsule-type adaptive sealant comprises the following steps:

[0052] Step 1: Select 6 ml of core material and 3.048 g of wall material, add them to 50 ml of low boiling point solvent, and form a completely miscible, uniform and stable oil phase solution by uniform stirring at 30°C. Weigh 2 g of emulsifier, add it to 98 ml of deionized water, and stir to prepare a 2 wt% emulsifier solution. Then, at 1000 rpm, slowly drop 50 ml of oil phase solution into 100 ml of water phase solution containing emulsifier, with a drop speed of 5 ml / min, to form an oil-in-water (O / W) emulsion.

[0053] Step 2: The formed emulsion system is evaporated at 500 rpm and a constant temperature of 25°C to remove the low-boiling point solvent. During the solvent evaporation process, the interfacial tension and surface energy drive the hydrophilic wall material to continuously migrate to the interface between the polysulfide rubber and water, and finally form microcapsules with liquid polysulfide rubber encapsulating the core material.

[0054] Step 3: After the solvent is completely evaporated, the remaining solution is subjected to high-speed centrifugation at 8000 rpm to obtain a precipitate, and the precipitate is fully washed with deionized water for 3 times, and then dried to obtain polysulfide rubber microcapsule powder.

[0055] Step 4: Compounding process, plasticizer adjustment: If 100g of microcapsule powder is taken, 35g of plasticizer (dibutyl phthalate) is added as a viscosity regulator of the sealant.

[0056] Tackifier addition: While stirring, add 7g of epoxy resin tackifier to ensure that the prepared sealant has good adhesion and construction performance.

[0057] Reinforcement agent introduction: Add 3g of reinforcing agent (such as silica or carbon black) to the mixed liquid and stir evenly. The addition of reinforcing agent will improve the mechanical strength and durability of the sealant.

[0058] Introduction of accelerator: Add 2 g of accelerator (diphenylguanidine) into the mixture, ensuring that it is evenly distributed to accelerate the vulcanization reaction.

[0059] Curing agent mixing: gradually add 28g of manganese dioxide curing agent to the microcapsule dispersion (add in 4 times, 7g each time, 5 minutes interval), and stir evenly. The stirring speed should be moderate to avoid microcapsule rupture and ensure that the curing agent is in full contact with the surface of the microcapsule.

[0060] The temperature during the mixing process was controlled to be no greater than 35°C to avoid excessively high temperatures causing microcapsule rupture or premature reaction of the curing agent.

[0061] Step 5: Control the curing process. Degas the mixed sealant in a vacuum box to remove bubbles introduced during the mixing process and prevent the formation of pores after curing.

[0062] Apply the degassed sealant to the target substrate surface and control the ambient temperature to 0°C.

[0063] -35℃ and humidity condition 40%-80% for vulcanization reaction. Ensure uniformity during curing to obtain uniform curing effect.

[0064] When the microcapsule sealant material prepared by the embodiment of the present invention is coated on parts, the coating thickness plays a crucial role and directly affects the sealing performance, mechanical strength, assembly difficulty and reliability of the final product.

[0065] If the sealant is too thin, it may not be able to completely cover the gap between the threads in terms of sealing performance, resulting in poor sealing or failure, and unable to overcome the corrosion and aging problems in the high temperature and high humidity marine environment; if the sealant is too thick, the sealant is easily squeezed out during the tightening process, which may lead to over-tightening on the one hand, and serious waste of sealant on the other hand. And if the glue is too thick, the friction will increase when the bolt is tightened, making the assembly process more difficult. On the contrary, if the coating is too thin, it will not provide enough resistance, causing the bolt to loosen more easily. Therefore, the appropriate coating thickness can provide the best sealing effect and thread locking performance, while extending the service life of the parts. Too thick or too thin coating may affect the tightening force, vibration resistance and sealing effect of the bolt.

[0066] Take 90 countersunk bolt HB1-129-514 as an example, the structure of 90 countersunk bolt is as follows: Figure 1 . According to the HB1-129-2002 bolt specification and the digital display vernier caliper, the distance from the bottom to the top of the thread is 0.8mm. The experiment tried to apply polysulfide microcapsule sealant on the HB1-129-5 14 bolt. Try to just cover, slightly overflow the bolt surface, just fill the bottom of the thread, and fill half to two-thirds of the thread depth. The three coating thicknesses range from 0.8-0.9mm, 0.1-0.2mm, and 0.4-0.5mm. When the coating thickness is about 0.8-0.9mm, just fill the thread and cover it to slightly overflow the top of the thread, after drying, when the M5 nut is screwed on, a lot of friction can be felt at the beginning of screwing in, which hinders the assembly of the nut, making the assembly process difficult to carry out easily. As the nut is screwed in, part of the polysulfide microcapsule sealant is squeezed from the screwed thread to the outside of the nut. This also leads to the waste of glue during coating. When the coating thickness is about 0.1-0.2mm, there is no obvious friction hindering the assembly of the nut during the process of screwing on the nut. This thickness of sealant gives the nut a lot of space to screw in, which will not cause great difficulties for the assembly of parts. However, if the coating thickness is too low, it may not be able to completely cover the gaps between the threads, and the sealing effect and thread locking performance are not enough to meet the service life and combat effectiveness of the aircraft in the high-salt and high-fog marine environment. When the coating thickness is about 0.4-0.5mm, from the process of screwing on the nut, the friction hindering the assembly of the nut is weak, and this coating thickness does not have much effect on the assembly of parts. A trace amount of polysulfide microcapsule sealant is squeezed to the outside of the nut and adheres between the thread surface and the outside of the nut, which can provide appropriate tightening force and anti-vibration performance, enhance the sealing effect, and will not cause waste of polysulfide microcapsule sealant.

[0067] In general, a coating thickness of about 0.4 mm is most suitable, which can provide the best sealing effect and thread locking performance, and extend the service life of the aircraft in the marine environment.

[0068] After the sealant was cured at different curing temperatures for 24 hours, the disassembly torque and breaking torque measured at 15°C were relatively low, 1.057N·m and 0.507N·m respectively. Because at lower temperatures, the chemical reaction rate is slower and the curing time may be longer. The torque value increases slowly, and it takes a long time to reach a higher torque value, reaching the maximum value at 25 days. The TBA and TP after curing at 35°C for 24 hours are 2.514N·m and 1.504N·m respectively.

[0069] The matching nuts were screwed into the dried coated bolts and placed at room temperature for curing for 4h, 8h, 16h and 18h, and the changes in torque were recorded as the curing time increased. The destructive torque and disassembly torque of the sealant after curing for 6h and 12h were smaller than those after curing for 18h and 24h, which were 0.945N·m, 0.683N·m and 2.070N·m, 1.055N·m respectively. The curing time was short, and the torque value during the curing process of the sealant gradually increased, so the torque value was relatively lower in a shorter curing time. As the curing time increased, the destructive torque and disassembly torque gradually increased, and gradually stabilized after curing for 18h, maintaining at around 3.591N·m and 2.246N·m. It can be seen that curing for more than 18h is the best, and it also meets the standard of complete curing within 24h.

[0070] The protection scope of the present invention is not limited to the above-mentioned embodiments. Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the scope of the present invention. If these changes and modifications fall within the scope of the claims of the present invention and their equivalents, the present invention is intended to include these changes and modifications.

Claims

1. A method for preparing a microcapsule-type adaptive sealant, characterized in that: The steps include: Step 1: Select liquid polysulfide rubber as the core material and polystyrene as the wall material, add them to the solvent, and form a completely miscible, uniform and stable oil phase solution by uniform stirring; weigh the emulsifier, add it to deionized water, and prepare an emulsifier solution with a concentration of 2wt% by stirring; then, at a set speed, drop the oil phase solution into the emulsifier solution to form an oil-in-water emulsion; Step 2: The formed emulsion system is evaporated at a set speed to remove the solvent; during the solvent evaporation process, the interfacial tension and surface energy drive the hydrophilic wall material to continuously migrate to the interface between the polysulfide rubber and water, and finally form microcapsules with liquid polysulfide rubber wrapped around the core material; Step 3: After the solvent is completely evaporated, the remaining solution is subjected to high-speed centrifugation to obtain a precipitate, and the precipitate is fully washed with deionized water and dried to obtain polysulfide rubber microcapsule powder; Step 4: Take the microcapsule powder, add plasticizer, tackifier, reinforcing agent, accelerator, curing agent in sequence and stir evenly; Step 5: Degas the mixed sealant in a vacuum box.

2. The method for preparing a microcapsule-type adaptive sealant according to claim 1, characterized in that: The mass ratio of the components in the first step is: core material: capsule wall: solvent: emulsifier = 2.5:1: 20-40: 0.6-0.

7.

3. The method for preparing a microcapsule-type adaptive sealant according to claim 1, characterized in that: In the first step, the solvent used is a low boiling point solvent, and the solvent that can be used includes dichloromethane.

4. The method for preparing a microcapsule-type adaptive sealant according to claim 1, characterized in that: In the first step, the rotation speed is set to 1000 rpm.

5. The method for preparing a microcapsule-type adaptive sealant according to claim 1, characterized in that: In the second step, the rotation speed is set to 500 rpm.

6. The method for preparing a microcapsule-type adaptive sealant according to claim 1, characterized in that: In the fourth step, the mass ratio of the microcapsule powder, the plasticizer, the tackifier, the reinforcing agent, the accelerator and the curing agent is 100:30-40:5-10:2-4:1-3:20-40.

7. The method for preparing a microcapsule-type adaptive sealant according to claim 1, characterized in that: In the fourth step, the plasticizer is dibutyl phthalate, the tackifier is epoxy resin, the reinforcing agent is silicon dioxide or carbon black, the accelerator is diphenylguanidine, and the curing agent is manganese dioxide.

8. The method for preparing a microcapsule-type adaptive sealant according to claim 1, characterized in that: The temperature during the mixing process in the fourth step is not greater than 35°C.

9. The method for preparing a microcapsule-type adaptive sealant according to claim 1, characterized in that: After the fifth step, the degassed sealant is applied to the target substrate surface and the vulcanization reaction is carried out by controlling the ambient temperature and humidity conditions.

10. The method for preparing a microcapsule-type adaptive sealant according to claim 9, characterized in that: When a 90° countersunk bolt is used as the target substrate, the sealant coating thickness is 0.4 mm to 0.5 mm.

Images