Preparation method and equipment of pH-sensitive microcapsules with controllable components

Abstract

The invention belongs to the technical field of metal corrosion prevention, and particularly relates to a preparation method and equipment of a component-controllable pH-sensitive microcapsule, and the preparation method comprises the following steps: dissolving a certain mass of an indicator and a pH-responsive polymer in an organic solvent to form a solution, the concentrations of the indicator and the pH-responsive polymer in the organic solvent being 1%-10% and 5%-10% respectively; and feeding the solution into a spray dryer through a peristaltic pump, carrying out spray drying treatment at a certain temperature and pressure, and obtaining the pH sensitive microcapsule loaded with the indicator in a collection bottle. According to the technology, long-time continuous production can be achieved, the requirement for selectivity of indicator molecules is not high, the technology can be used for coating multiple different types of indicator molecules, the application universality of a self-early-warning coating is improved, and the stirring efficiency and the processing speed are greatly improved through revolution and autorotation of the two stirring rods.

Description

Technical Field

[0001] The invention relates to the technical field of metal anticorrosion, and in particular to a preparation method and equipment of pH-sensitive microcapsules with controllable ingredients. Background Art

[0002] Corrosion is an important form of material failure, and the economic losses caused by corrosion each year account for 3% to 5% of GDP. In order to delay corrosion and extend the service life of materials, people have developed a variety of anti-corrosion methods and means for different corrosion environments or corrosion processes. Among the many anti-corrosion means, organic coatings have become the most widely used anti-corrosion means due to their advantages such as low construction difficulty, excellent anti-corrosion effect, and easy combination with other anti-corrosion means. However, it is inevitable that some minor damage will occur in the organic coating during the preparation or service process. Studies have shown that these minor damage sites will become the preferred path for the transmission of corrosive media in the coating. When the corrosive medium reaches the surface of the metal substrate along the damaged site in the coating, it will cause corrosion of the metal substrate. The corrosion process will reduce the bonding force between the coating and the metal substrate, causing the coating to gradually peel off from the surface of the metal substrate and lose protection for the site. In order to improve the reliability and safety of the coating service, it is necessary to promptly discover and deal with the defects of the coating, ensure the safe service of the coating, extend the service life of the coating, and reduce the cost of anti-corrosion.

[0003] The main difficulty in dealing with coating defects is how to detect coating defects at low cost and high efficiency. People have developed a variety of detection technologies for coating damage, such as electrochemical measurement, thermal imaging, ultrasonic radiation, etc., but there are still problems such as expensive and complex equipment, low detection efficiency, and inability to monitor coating defects in situ. In order to be able to observe the defects in the coating more intuitively, dye molecules or fluorescent probes are often introduced into the coating as indicators to prepare self-warning coatings. When the self-warning coating is damaged, obvious color changes or fluorescence intensity changes will appear at the damaged site, which plays a warning function. The self-warning coating can warn the location of coating defects without human intervention, and send out warning signals at the early stage of corrosion, so as to facilitate timely and effective measures to reduce the harm caused by corrosion and effectively avoid the occurrence of severe corrosion.

[0004] At present, some related technologies involving self-warning coatings have been published. For example, the Chinese patent with application number 202311074084.9 discloses a corrosion self-warning coating material and its preparation method. The invention uses rhodamine B hydrazide to modify the surface of the composite fluorescent probe for iron ion response, and loads it in a nano-silica container, which is applied to the anti-corrosion coating on the surface of steel. When there is no corrosion, the fluorescence is in a closed state. Once the steel undergoes early slight corrosion, the generated iron ions will open the spiro ring of the modified rhodamine B hydrazide, presenting a fluorescence-on state, which is convenient for detecting the corrosion of steel under the coating through fluorescence; while the fluorescence appears, the naked eye can also observe an obvious orange-red color, thereby realizing the fluorescence / colorimetric dual-channel detection and self-warning of the coating for corrosion ions. The surface of the composite fluorescent probe is loaded with nano-silica, which can not only avoid premature reaction between the fluorescent probe and the coating components and failure, improve its compatibility with the coating, but also enhance the shielding protection and mechanical properties of the coating, and extend the service life of the coating. The Chinese patent with application number 202110767459.4 discloses a method for preparing salt-responsive polyaniline microcapsules and self-warning coatings. The invention uses polyaniline microcapsules to encapsulate fluorescent small molecules, and uses polyaniline microcapsules to achieve controllable release of fluorescent molecules in salt solutions. After the polyaniline microcapsules are implanted into the coating, a self-warning coating is obtained, and the coating is artificially destroyed and immersed in salt water. It is difficult for the naked eye to distinguish the scratches under white light, but when ultraviolet light is used to irradiate it, the scratches on the coating will emit obvious bright green fluorescence, so that cracks that were originally invisible to the naked eye can be captured, realizing the self-warning function of the coating.

[0005] There are still some problems with the above technologies: 1. The composition of the microcontainer is uncontrollable. In the above technology, microcontainers such as microcapsules or silica are used to load indicator molecules and release them under specific conditions. Among them, the microcontainer used to load the indicator is the key to the application of this technology. In the currently used microcontainers, the amount of indicator cannot be accurately adjusted according to needs, that is, the composition of the microcontainer is uncontrollable, which may affect the amount of microcontainer and the self-warning effect.

[0006] 2. Microcapsules are commonly used microcontainers for loading indicators. However, complex chemical reactions usually occur during the synthesis of microcapsules. On the one hand, this limits the coating of indicator molecules. Some indicators may not be able to be coated or have a low loading amount. On the other hand, the process involves complex chemical reaction parameters, which makes the microcapsule preparation process complicated and limits the development of this technology.

[0007] 3. When using inorganic materials such as silica as containers, the compatibility of inorganic microcontainers with organic coatings is poor, which may have an adverse effect on the coating performance, which also limits the application of this technology.

[0008] In view of the problems existing in the above-mentioned technologies, the present invention adopts spray drying technology to realize the controllable preparation of the components of microcapsules, and the existing pharmaceutical mixing equipment has poor mixing strength and low mixing and stirring efficiency.

[0009] Therefore, we proposed a preparation method and equipment of pH-sensitive microcapsules with controllable ingredients to solve the above problems. Summary of the invention

[0010] The purpose of the present invention is to solve the shortcomings of the prior art and to propose a preparation method and equipment for pH-sensitive microcapsules with controllable ingredients.

[0011] In order to achieve the above object, the present invention adopts the following technical solutions: A method for preparing a pH-sensitive microcapsule with controllable composition, wherein a certain mass of an indicator and a pH-responsive polymer are dissolved in an organic solvent to form a solution, wherein the concentrations of the indicator and the pH-responsive polymer in the organic solvent are 1%-10% and 5%-10%, respectively; The above solution is introduced into a spray dryer through a peristaltic pump, spray-dried at a certain temperature and pressure, and pH-sensitive microcapsules loaded with an indicator are obtained in a collection bottle; The selected pH-responsive polymer includes one of polylactic acid and Eudragit, the selected organic solvent includes one or more low-melting-point organic solvents such as ethanol, acetone, dichloromethane, tetrahydrofuran, etc., and the composition of the pH-sensitive microcapsule can be adjusted by changing the ratio of the indicator to the pH-responsive polymer.

[0012] Preferably, the spray drying process must be carried out under nitrogen protection conditions, the spray drying inlet temperature is 60-120°C, the outlet temperature is 50-70°C, and the nozzle pressure is 0.4-0.6 Mpa.

[0013] Preferably, the microcapsules and the aqueous polymer resin are uniformly mixed by stirring, the mass fraction of the pH-sensitive microcapsules in the polymer resin is 1%-5%, the stirring speed is 800-1200rpm, and the stirring time is 25-40min; after degassing for 30min, it is coated on the metal substrate and cured to obtain the desired self-warning coating.

[0014] Preferably, the selected water-based polymer resin includes one of water-based polyurethane resin, water-based acrylic resin, and water-based epoxy resin. When the selected resin is a single-component resin, the resin and the microcapsules can be directly mixed; when the selected resin is a two-component resin, the resin and the microcapsules must be mixed first, and then mixed with the curing agent. The coating is performed by scraping, spin coating or spraying, and the coating thickness is 100-200 μm.

[0015] The present invention also includes a preparation device for pH-sensitive microcapsules with controllable ingredients, including a stirring barrel, a bracket fixedly connected to the stirring barrel, a fixed rod fixedly connected to the bracket, a rotating sleeve rotatably sleeved on the fixed rod, a first bevel gear fixedly sleeved on the rotating sleeve, an extension plate fixedly connected to the bracket, a second rotating rod rotatably connected to the extension plate, a second rotating rod fixedly connected to the second rotating rod, the second bevel gear meshing with the first bevel gear, and a motor fixedly installed on the extension plate to drive the second rotating rod to rotate.

[0016] Preferably, a rotating rod is fixedly sleeved on the rotating sleeve, the lower end of the rotating rod is rotatably connected to two first rotating rods correspondingly arranged on the left and right, the lower end of the fixed rod is fixedly connected to the second gear, the lower ends of the two first rotating rods are fixedly connected to the first gear, and the two first gears are meshed with the second gear.

[0017] Preferably, the lower ends of the two first gears are fixedly connected with stirring rods.

[0018] Preferably, the rotating rod 5 is provided with two symmetrically arranged scraper mechanisms, and the scraper mechanisms include a support plate 15, the support plate 15 is fixedly connected to the rotating rod 5, the lower end of the rotating rod 5 is fixedly connected to a connecting rod 16, and two connecting columns 17 are fixedly connected to the connecting rod 16, and the two connecting columns 17 are both slidably sleeved with a sliding box 18, and the two connecting columns 17 are both sleeved with a spring 19, one end of the two springs 19 is fixedly connected to the connecting rod 16, and the other end of the two springs 19 is fixedly connected to the corresponding sliding box 18, the two sliding columns 17 are fixedly connected with a stop block 20, and the two sliding boxes 18 are fixedly connected with a mounting block 21, and the front ends of the two mounting blocks 21 are commonly fixedly connected to a scraper 22, and the scraper 22 has two mounting holes 23.

[0019] Compared with the existing technology, the advantages of this method and device are: 1. Spray drying technology has the characteristics of long-term continuous production, which overcomes the problems of complex preparation process and low yield in the preparation of microcapsules to a certain extent. At the same time, the preparation of microcapsules by this method does not involve chemical changes, so the selectivity of indicator molecules is not high, and it can be used to coat a variety of different types of indicator molecules, which improves the wide application of self-warning coatings. In addition, this technology selects high molecular polymers as microcapsule wall materials, which have good compatibility with the coating and have little effect on the coating performance.

[0020] 2. The raw materials in the mixing barrel are stirred and mixed by the two first gears revolving around the second gear, and the two first gears revolve around the second gear while rotating, driving the two stirring rods to revolve and rotate at the same time, greatly improving the stirring efficiency and the processing speed.

[0021] In summary, this technology can be used for long-term continuous production, does not have high requirements on the selectivity of indicator molecules, can be used to coat a variety of different types of indicator molecules, and improves the wide application of self-warning coatings. The equipment greatly improves the stirring efficiency and processing speed by rotating the two stirring rods while orbiting. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is the morphology of microcapsules prepared by spray drying technology; Figure 2 This is the infrared spectrum of Eudragit E-E100, phenolphthalein, and microcapsules; Figure 3 is the UV-visible absorbance curve of phenolphthalein; Figure 4 is the concentration-absorbance calibration curve of phenolphthalein; Figure 5 is the release curve of microcapsules under different pH conditions; Figure 6 is the mass ratio of phenolphthalein / Eudratrol E-E100 before and after spray drying; Figure 7 The color change mechanism of phenolphthalein under alkaline conditions; Figure 8 This is the color change diagram of the damaged coating; Fig. 9 The present invention is a three-dimensional schematic diagram of a preparation method of pH-sensitive microcapsules with controllable ingredients and a stirring device in the device.

[0023] Fig.10 The present invention is a partial three-dimensional schematic diagram of a preparation method of pH-sensitive microcapsules with controllable ingredients and a stirring device in the device.

[0024] Fig.11 The invention is a three-dimensional schematic diagram of a method for preparing pH-sensitive microcapsules with controllable ingredients and a scraper mechanism in a stirring device in the device.

[0025] In the figure: 1 a mixing barrel, 2 a bracket, 3 a fixing rod, 4 a rotating sleeve, 5 a rotating rod, 6 a first rotating rod, 7 a first gear, 8 a second gear, 9 a first bevel gear, 10 an extension plate, 11 a second rotating rod, 12 a second bevel gear, 13 a motor, 14 a mixing rod, 15 a supporting plate, 16 a connecting rod, 17 a connecting column, 18 a sliding box, 19 a spring, 20 a blocking block, 21 a mounting block, 22 a scraper, and 23 a mounting hole. DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0027] Reference Figure 1-Figure 11 , a preparation method and equipment of pH-sensitive microcapsules with controllable ingredients, When using the present invention, a method for preparing pH-sensitive microcapsules with controllable ingredients is characterized in that it specifically includes the following steps: dissolving a certain mass of phenolphthalein indicator and Eudragit E-E100 in acetone to form a solution, wherein the concentrations of phenolphthalein and Eudragit E-E100 in acetone are 5% and 8%, respectively. The above solution enters the spray dryer through a peristaltic pump, and the spray drying process is carried out under nitrogen protection conditions. The inlet temperature of the spray drying is 80°C, the outlet temperature is 60°C, and the nozzle pressure is 0.5 Mpa. The pH-sensitive polylactic acid microcapsules loaded with phenolphthalein are obtained in the collection bottle. Please refer to Figure 1 The obtained microcapsules are regular spherical in shape with an average particle size of about 3.5 μm. Figure 2 After spray drying, the characteristic peaks in the microcapsules were consistent with those in phenolphthalein and Eudragit E-E100, and no new infrared spectrum characteristic peaks appeared, indicating that no chemical reaction occurred during the spray drying process, and the changes involved in the process were the volatilization of acetone and the formation of microcapsules.

[0028] See also Figure 3 The UV-visible absorption spectrum of phenolphthalein shows that phenolphthalein has a characteristic absorption peak at 230nm. Figure 4 According to the different intensities of the characteristic peaks of phenolphthalein at different concentrations, the concentration-absorbance calibration curve of phenolphthalein was obtained. Based on this, the concentration of phenolphthalein can be obtained by measuring the absorbance of phenolphthalein of unknown concentration. Figure 5 , the microcapsules were placed in solutions with different pH values, and the microcapsules showed obvious pH-sensitive release behavior. Under neutral conditions, phenolphthalein was basically not released, but under acidic and alkaline conditions, a large amount of phenolphthalein was released in a short time. This is because the molecules of Eudragit E-E100 are rich in ester bonds, which undergo hydrolysis reactions under acidic or alkaline conditions, causing the long-chain polymers to gradually decompose into small molecules. Along with the destruction of the molecular structure, the skeleton of the microcapsules dissolved, the microcapsules gradually destroyed, and the phenolphthalein molecules loaded therein were also released and played a role, thus showing pH-sensitive release function.

[0029] See also Figure 6, the mass ratio of phenolphthalein / Eudratrol E-E100 in the raw material and microcapsules. The mass ratio of phenolphthalein / Eudratrol E-E100 before and after spray drying remained basically unchanged. Therefore, the composition of microcapsules can be controlled by changing the mass ratio of phenolphthalein / Eudratrol E-E100 before spray drying.

[0030] A method for preparing a self-warning coating using pH-sensitive microcapsules, characterized in that the microcapsules and water-based epoxy resin are mixed evenly by stirring, and the proportion of the microcapsules in the coating is 3%. The stirring speed is 1000rpm, and the stirring time is 30min. After uniform dispersion, the water-based polyamide curing agent is added thereto, stirred and degassed for 30min, and then coated on a Q235 carbon steel substrate by scraping, and cured to obtain the desired self-warning coating, and the resulting coating thickness is 150μm.

[0031] When the self-warning coating is damaged, the Q235 steel below the damaged coating undergoes electrochemical corrosion. As the corrosion progresses, the pH value in the anode area gradually decreases, while the pH value in the cathode area gradually increases. The change in pH near the corrosion area causes the microcapsules to gradually decompose and release the encapsulated phenolphthalein. Figure 7 When the pH of the solution is weakly alkaline, a quinone ring is formed in the phenolphthalein molecule, and the quinone ring forms a conjugated system with the benzene ring, so the color changes. See also Figure 8 , the coating damaged area undergoes obvious color changes, thus achieving color early warning of the coating damaged area.

[0032] A preparation method and equipment of pH-sensitive microcapsules with controllable ingredients, comprising a stirring barrel 1, a bracket 2 is fixedly connected to the stirring barrel 1, a fixed rod 3 is fixedly connected to the bracket 2, a rotating sleeve 4 is rotatably sleeved on the fixed rod 3, a first bevel gear 9 is fixedly sleeved on the rotating sleeve 4, an extension plate 10 is fixedly connected to the bracket 2, a second rotating rod 11 is rotatably connected to the extension plate 10, a second rotating rod 11 is fixedly connected to the second rotating rod 11, the second bevel gear 12 is meshed with the first bevel gear 9, a motor 13 for driving the second rotating rod 11 to rotate is fixedly installed on the extension plate 10, the second rotating rod 11 is driven to rotate by the motor 13, the second bevel gear 12 is driven to rotate, the second bevel gear 12 drives the first bevel gear 9 to rotate, and thus drives the rotating sleeve 4 to rotate; A rotating rod 5 is fixedly sleeved on the rotating sleeve 4, and the lower end of the rotating rod 5 is rotatably connected to two first rotating rods 6 correspondingly arranged on the left and right. The lower end of the fixed rod 3 is fixedly connected to a second gear 8, and the lower ends of the two first rotating rods 6 are fixedly connected to first gears 7, and the two first gears 7 are meshed with the second gear 8. When the rotating sleeve 4 rotates, the two first rotating rods 6 are driven to revolve around the second gear 8, and the two first gears 7 revolve around the second gear 8 while rotating. The lower ends of the two first gears 7 are fixedly connected to stirring rods 14, and the raw materials in the mixing barrel 1 are stirred and mixed by the two first gears 7 revolving around the second gear 8. The two first gears 7 revolve around the second gear 8 and rotate at the same time, driving the two stirring rods 14 to revolve and rotate at the same time, thereby greatly improving the stirring efficiency and the processing speed.

[0033] The rotating rod 5 is provided with two symmetrically arranged scraper mechanisms, and the scraper mechanisms include a support plate 15, and the support plate 15 is fixedly connected to the rotating rod 5. The lower end of the rotating rod 5 is fixedly connected to a connecting rod 16, and the connecting rod 16 is fixedly connected to two connecting columns 17. The two connecting columns 17 are both slidably sleeved with a sliding box 18, and the two connecting columns 17 are sleeved with springs 19, one end of the two springs 19 is fixedly connected to the connecting rod 16, and the other end of the two springs 19 is fixedly connected to the corresponding sliding box 18, and the two sliding columns 17 are fixedly connected with a stop block 20, and the two sliding boxes 18 The two mounting blocks 21 are fixedly connected with mounting blocks 21, and the front ends of the two mounting blocks 21 are commonly fixedly connected with scrapers 22. The scrapers 22 are provided with two mounting holes 23. The scrapers 22 are fixed on the two mounting blocks 21 through the two mounting holes 23 using bolts and other tools. The two springs 19 exert elastic force on the two sliding boxes 18, so that the scrapers 22 in the two scraper mechanisms are pressed against the inner wall of the mixing barrel 1. When the rotating rod 5 rotates, the two scraper mechanisms are driven to rotate. When stirring, the two scraper mechanisms can scrape off the raw materials adhering to the inner wall of the stirring barrel 1, so that the raw materials in the mixing barrel 1 are fully stirred and mixed, thereby improving the stirring and mixing effect.

[0034] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for preparing pH-sensitive microcapsules with controllable ingredients, characterized in that: The following steps are involved: A certain mass of indicator and pH-responsive polymer are dissolved in an organic solvent to form a solution, wherein the concentrations of the indicator and pH-responsive polymer in the organic solvent are 1%-10% and 5%-10%, respectively; The above solution is introduced into a spray dryer through a peristaltic pump, spray-dried at a certain temperature and pressure, and pH-sensitive microcapsules loaded with an indicator are obtained in a collection bottle; The selected pH-responsive polymer includes one of polylactic acid and Eudragit, the selected organic solvent includes one or more low-melting-point organic solvents such as ethanol, acetone, dichloromethane, tetrahydrofuran, etc., and the composition of the pH-sensitive microcapsule can be adjusted by changing the ratio of the indicator to the pH-responsive polymer.

2. The method for preparing a pH-sensitive microcapsule with controllable composition according to claim 1, characterized in that: The spray drying process must be carried out under nitrogen protection conditions. The inlet temperature of the spray drying is 60-120°C, the outlet temperature is 50-70°C, and the nozzle pressure is 0.4-0.6 Mpa.

3. The method for preparing a pH-sensitive microcapsule with controllable composition according to claim 1, characterized in that: The microcapsules and the aqueous polymer resin are mixed evenly by stirring, the mass fraction of the pH-sensitive microcapsules in the polymer resin is 1%-5%, the stirring speed is 800-1200rpm, and the stirring time is 25-40min; after degassing for 30min, it is coated on the metal substrate and cured to obtain the desired self-warning coating.

4. The method for preparing a pH-sensitive microcapsule with controllable composition according to claim 3, characterized in that: The selected water-based polymer resin includes one of water-based polyurethane resin, water-based acrylic resin and water-based epoxy resin. When the selected resin is a single-component resin, the resin and the microcapsule can be directly mixed; when the selected resin is a two-component resin, the resin and the microcapsule need to be mixed first, and then mixed with the curing agent. The coating is carried out by scraping, spin coating or spraying, and the coating thickness is 100-200 μm.

5. An apparatus for use in the method for preparing the pH-sensitive microcapsules with controllable ingredients according to any one of claims 1 to 4, comprising a stirring barrel (1), characterized in that: The mixing barrel (1) is fixedly connected to a bracket (2), the bracket (2) is fixedly connected to a fixed rod (3), a rotating sleeve (4) is rotatably sleeved on the fixed rod (3), a first bevel gear (9) is fixedly sleeved on the rotating sleeve (4), an extension plate (10) is fixedly connected to the bracket (2), a second rotating rod (11) is rotatably connected to the extension plate (10), a second rotating rod (11) is fixedly connected to the second rotating rod (11), the second bevel gear (12) is meshed with the first bevel gear (9), and a motor (13) is fixedly mounted on the extension plate (10) for driving the second rotating rod (11) to rotate.

6. The device for preparing a method for pH-sensitive microcapsules with controllable composition according to claim 5, characterized in that: A rotating rod (5) is fixedly sleeved on the rotating sleeve (4), and the lower end of the rotating rod (5) is rotatably connected to two first rotating rods (6) arranged correspondingly on the left and right. The lower end of the fixed rod (3) is fixedly connected to a second gear (8), and the lower ends of the two first rotating rods (6) are both fixedly connected to a first gear (7), and the two first gears (7) are both meshed with the second gear (8).

7. The device for preparing a method for pH-sensitive microcapsules with controllable composition according to claim 6, characterized in that: The lower ends of the two first gears (7) are both fixedly connected to a stirring rod (14).

8. The device for preparing a method for preparing pH-sensitive microcapsules with controllable composition according to claim 7, characterized in that: The rotating rod 5 is provided with two symmetrically arranged scraper mechanisms, which include a support plate 15, which is fixedly connected to the rotating rod 5, a connecting rod 16 is fixedly connected to the lower end of the rotating rod 5, two connecting columns 17 are fixedly connected to the connecting rod 16, a sliding box 18 is slidably sleeved on the two connecting columns 17, springs 19 are sleeved on the two connecting columns 17, one end of the two springs 19 is fixedly connected to the connecting rod 16, and the other end of the two springs 19 is fixedly connected to the corresponding sliding box 18, a blocking block 20 is fixedly connected to the two sliding columns 17, and a mounting block 21 is fixedly connected to the two sliding boxes 18, a scraper 22 is fixedly connected to the front end of the two mounting blocks 21, and two mounting holes 23 are provided on the scraper 22.

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