Microcapsules for self-healing coatings and preparation technology thereof

With the development
and progress of material technology and large-scale integrated circuit technology, the U.S. military first put forward the idea and concept of intelligent self-healing materials and structures, and then carried out a large-scale study. In recent years, foreign research institutions and some companies have carried out in-depth research on the technology, there are some self-healing automotive coating products come out and get a certain application. Domestically, since the beginning of this century, a few research institutions have begun to study self-healing composites

.
For example, the Zhang Mingqiu task force of Sun Yat-sen University designed and synthesized a series of implantable and self-healing polymer materials using the theory and methods of polymer chemistry, polymer physics, materials mechanicals and other disciplines, and proposed self-healing strategies for typical thermostatic and thermoplastic polymer materials. In-depth study of the relevant synthesis routes, formulation optimization, preparation process, material structure and performance, self-healing micro-mechanism, use stability, etc. , for the application of such self-healing polymer materials provides a sufficient basis.
most mature self-healing technology is based on the microcapsule system of the technical route. Microcapsules system is a composite material technology, in the solid or liquid particles on the surface of a stable polymer membrane to form a nuclear shell, microcapsules technology in the substation implanted microcapsules, under the role of external forces, the substation material break, capsule material release, in the role of gap siphon, repair material full of cracks, complete the self-healing process. At present, the research on self-healing materials at home and abroad is mainly limited to solvent-based system, the research on water-based system is completely blank, and with the increasing attention to health and the continuous improvement of government environmental protection regulations, water-based coatings become an inevitable trend. Therefore, the study of water-like system self-healing coating has far-reaching technical and market value.
this study used suitable monosome and polymerization methods to prepare microcapsules containing repair agents, and prepared microcapsules, main resins, water-based isocyanate curing agents and pigments to prepare self-healing intelligent coatings.
preparation of
microcapsules in the experimental part
12 g urea and 24 g formaldehyde solution (37%) were added to a 250 mL three-mouth bottle filled with mechanical stirring. After the complete dissolution of urea, the pH of the solution is slowly adjusted to about 8 with triethanolamine, heating up to 50 to 65 degrees C at a heating rate of 5 degrees C/min, and maintaining 1h after heating up to obtain a prepolymer of urea and formaldehyde. After the product cools naturally, the 30 g water-based isocyanate curing agent XP 2655 is slowly added to the above solution and the speed is adjusted to 350 r/min. After stirring 20 to 30 min, slowly adjust the pH of the solution to 2 to 3 with 10% thin H2SO4 solution. Heat up to 60 to 65 degrees C at a heating speed of 2 degrees C/min, maintain 3 to 4 h, and the reaction is over. The reaction was cleaned 5 to 6 times with deionized water at 60 degrees C, and the white microcapsules were dried after filtration.
microcapsules base self-healing coating preparation
according to the design formula of the raw materials stirred and dispersed evenly to get part A. Mixing part A with the water-based isocyanate curing agent B (Bayhydur XP2655) is well mixed, the coating method is used, and 30 min film is baked at 80 degrees C.
Chemical structure analysis of microcapsules and self-healing coatings
(1) microcapsules
using FT-IR to analyze the chemical structure of microcapsules, to test the chemical structure of KBr after pressing with polypropyl formaldehyde powder, and to test the chemical structure of KBr with microcapsule powder. Reactants, products and microcapsules are compared and analyzed according to infrared spectra.
(2) microcapsules
using QUANTA200 scanning electron microscopes (SEMs) and XSZ-7G optical microscopes (OM) to characterize the surface appearance of microcapsules, SEM testing The method is to dry the microcapsules powder, with double-sided glue glue on the homemade sample rack, after gold spray observation, OM test method is to microcapsules emulsion 1 to 2 drops evenly applied to the surface of the slide, observe the surface shape of the microcapsules and monitor the formation process of microcapsules.
(3) microcapsules-based self-healing coating performance test
coating performance is tested according to the corresponding national standard method.
results and discussion of
microcapsules structure and physical appearance
former resin preparation
Figure 1 formaldehyde resin infrared map
as can be seen from Figure 1, N-H's surface curved vibration absorption peak at 1548 cm-1; At 2964 cm-1 is the absorption of saturated C-H telescopic vibration; at about
3410 cm-1, the telescopic vibration absorption peak of hydroxymethylene-OH is the result of hydrogen bonding effect in the molecular structure; C-O's telescopic absorption vibration peak is located at 1642 cm-1, and the infrared spectrograph indicates that the synthetic polyformaldehyde may contain ether bonds. It is proved that the polycelue formaldehyde material has been successfully prepared.
isocyanate resin wrapped isocyanate curing agent
Figure 2 microcapsules infrared map
a. isoalde resin; b isocyanate curing agent; c. isocyanate resin encapsulated curing agent microcapsules
Figure 2 a is the infrared absorption curve of the polycycline formaldehyde sac wall. Figure b shows the infrared spectrum of Bayhydur XP 2655 curing agent. In the figure, it can be seen that 2270cm-1 is the telescopic vibration absorption peak of the NCO group in the curing agent, and 1693cm-1 is the telescopic vibration peak of N-CO-N in the curing agent, which is a typical absorption peak in hydro-modified HDI modified trimer;
the telescopic vibration absorption peak of the NCO group appeared at 2270cm-1 in Figure c, indicating that the polyheterate curing agent was successfully encapsulated in the microcapsules. The telescopic vibration absorption peak of the NCO group is less than the curing agent itself, which is due to the reaction of the NCO group with the water in the system and hydroxyl in the prejudehyde prejudehyde during the preparation of the microcapsules, consuming a portion of the NCO group.
microcapsules are characterized
figure 3 shows photos of acetaldehyde resin and microcapsules coated with polyseocyanate, both of which are white powdered solids.
Figure 3 Microcapsules Appearances
1: Acetaldehyde Resin; 2 : Acetaldehyde Resin Encased isocyanate curing agent
Figure 4 shows a scanning electroscope photo of the ethyl acetaldehyde resin and a microcapsules encased with polysylyanate, respectively. As can be seen from the figure, both products are speral structures, in which the surface of the small ball that is not covered with polycycyanate core material is smoother, and many small ball parts of the microcapsules covered with polycyanate have flocculants, which is due to the acidification process of polycyanate and arbondehyde resin pre-polymer process, some gel particles have not yet been able to migrate to isocyanate drop surface between each other.
addition, part of isocyanate in the water phase with the water side reaction, resulting in isocyanate curing agent condensation, the formation of a condensate, distributed in the vicinity of the successful clad ball.
Figure 4 Microcapsules SEM Photo
1: Acetaldehyde Resin; 2 : The appearance, average particle size and storage stability of the microcapsules prepared by isocyanate curing agent
wrapped in acetaldehyde resin are shown in the table below. The data in the table indicate that the prepared small test products meet the project target requirements.
project product technical indicators
microcapsules-based coating performance testing
using homemade water-based hydroxypropyl acrylic resin, with water-based isocyanate curing agent and corresponding additives, add a reasonable amount of coating with curing agent microcapsules, preparation of microcapsules-based water-based coatings. In order to determine the dispersion of microcapsules in the coating, optical microscopes are used to observe the composite membrane directly. Figure 5 shows an optical microscope photo of a water-based paint film with microcapsules added. The microcapsules in the figure were more uniformly dispersed, there was no reunion phenomenon, and the dispersion was better. Because microcapsules can be evenly dispersed in polymers, they are ideal for preparation into composites and are highly practical.
Figure 5 Microcapsule-based water-based coating surface optical microscope photo
film performance test
from the data in the table above can be seen, the addition of microcapsules of water-based polyurethane coating cured paint film smooth, high hardness, good adhesion, excellent impact resistance, water resistance and ethanol resistance, excellent alkalinity resistance, microcapsules added to other properties of the coating has no greater impact. From the above discussion, it can be seen that the microcapsules prepared in this paper can be evenly dispersed in the coating, no reunion phenomenon.
self-healing test using a surgical knife on the microcapsule-based coating scratch, the naked eye to observe the repair effect. Custom repair performance 1 to 4 levels, 1 level for basic no repair, 4 levels for complete repair. After experimental verification, it is found that after 12h repair, the scratches begin to heal, reaching level 3 effect, with good self-healing function.
In conclusion
the microcapsules synthesis process was studied and discussed through experiments, which provided an important reference for the synthesis process conditions and structural properties of the formation of microcapsules by polycep formaldehyde cladding of suitable materials, and the microcapsules structure and performance were indicated, and microcapsules products were successfully prepared; The use of water-based hydroxypropyl acrylic resin as the main resin, with water-based isocyanate curing agent, add the appropriate amount of additives, and then add the prepared microcapsules, get microcapsules-based water-based self-healing paint;
author of the
(CNOOC Changzhou Environmental Protection Coatings Co., Ltd., Changzhou, Jiangsu Province)
the full contents of the "Coatings and Protection" 2020 No. 6
.