A study on the preparation and performance of a self-healing UV-cured coating.

Li Yaqing, Tan Jiawei, Gu Hao, Jin Biqing, Shenzhen University of Science and Technology New Materials Co., Ltd.
Guo Xiang, Zhang Zongbo, Institute of Chemistry of the Chinese Academy of Sciences
Summary
developed a self-healing function coating based on ultraviolet light (UV) curing technology, discussed the effects of various additives on self-healing function in the formulation optimization process, analyzed the self-healing function of the coating and studied its microstructure structure. This paper also introduces the application technology and engineering case of the coating, and looks forward to its development prospects.
01
coatings are indispensable materials for national production and development and are widely used in construction, home, industrial products and other fields

. Traditional coatings are generally based on organic solvents as a dispersion medium, and organic solvents are mostly toxic, flammable and harmful to the human body. With the restriction of volatile organic compounds (VOC) and the control of environmental pollution, the development of environmentally friendly coatings has become a hot spot in the field of coating research. Ultraviolet (UV) curing coatings with fast curing speed, high production efficiency, less investment in equipment, low curing temperature, excellent performance, less environmental pollution and other advantages, in recent years has been widely used, UV curing is an efficient, environmentally friendly, energy-saving coating preparation technology, the use of the principle of the coating is called UV coatings, such coatings in ultraviolet lamps can be cured into film for a short period of time, and show excellent paint performance. UV curing technology is regarded as a new technology for green industry in the 21st century because of its "5E" characteristics (efficient, economical, skill, high adaptability and environment-friendly).
UV curing coating is the essence of polymer-based composite materials, such materials in the construction and use of the process is vulnerable to shock and damage, so that the coating's physical properties, stability and other reduced, the protection of the substrate is very little. In addition to material damage caused by strong shocks, it is more common to have micro-damage to the material, which is often difficult to visually detect and has unpredictable consequences for the substrate. In recent years, scientists have established self-healing models of materials, which enable damage to materials, especially those that cannot be detected internally, to be repaired to a certain extent without the use of plus repair materials, which is important for maintaining the mechanical strength of the material, eliminating hidden dangers and extending service life. The application of self-healing technology to the field of UV-cured coatings results in self-healing UV-cured coatings, which have self-healing function after damage, or self-healing function under certain conditions.
With the continuous progress of material science, self-healing coatings in theoretical research and a new development of traditional coatings, in practical applications have been rapid development, this paper aims to start from the basic theory of self-healing coatings concept, through chemical modified means, combined with UV curing technology, optimize product formulation, develop a UV curing coating with self-healing function, which is to promote the UV curing industry technology level is of positive significance.
02 Experimental part
2.1 Raw materials, reagents and instruments
raw materials and reagents:
heteroesters, isoflavone diocyanate (IPDI), national pharmaceutical reagents;
acrylic hydroxyethyl ethyl esters (HEA), East Asian synthesis;
parabens, organotin catalysts, Beringweed reagents;
α-hydroxycycline phenylbenzene (Irgacure 184), Tianjin Kuji;
ethylene trihydroxymethyl propylene tripropylate, toluene, diethylene, butyl ketones, national drug tests.
solvents or monosomes are pure, un distilled, and used directly.
main instruments and equipment:
98-1-B type electronic thermostat, Tianjin Test Instruments Co., Ltd.;
Electronic Balance, Shanghai Puchun Metering Instrument Co., Ltd.;
DHG-9023A type electric thermostat blowing drying box, Shanghai Jinghong Experimental Equipment Co., Ltd.;
XD-B400 high-speed dispersion machine, Shanghai Mu Xuan Industrial Co., Ltd.;
Fourier Transform Infrared Spectrometer (FTIR), Bruker Corporation;
Field Launch Scan Electron Microscope (SEM), TormoS-4800;
Atomic Force Microscope (AFM), Brukerfimoode 8.
2.2 Resin Synthesis
adds a certain amount of heteroesters, polyether polyols, HEA, stirring 15 min and then adding a certain amount of catalysts and polymer inhibitors to the reaction bottles equipped with reflow condensers, water disinfectants, agitators and thermometers. Heating heating and control temperature between 60 to 80 degrees C, drip plus IPDI, insulation reflow 5h, FTIR detection system NCO group content, when the NCO base group characteristic absorption peak disappears, add diluted monosome, discharge for the finished UV resin.
2.3 Coating Formula Design
In accordance with the requirements of GB 18445-2012 standard product indicators, the self-healing coatings have been designed and optimized. With the above target resin as the main film polymer, add the appropriate amount of leveling agent, dilution monomer, ultraviolet curing agent, etc., with coating after spraying, the substrate is ABS plastic plate, the reference formula is shown in the table as follows:
03 results and discussion
self-healing is essentially a polymer The non-equilibrium deformation process of the material, i.e. the molecular relaxation process, leads to a deformation response, which is between elastic deformation and viscous deformation, or a combination of the characteristics of the elastic deformation of the polymer system and the viscous deformation, that is, it is a combination of solid elastomer deformation subject to Hulk's law and liquid viscosity subject to Newton's law. The self-healing properties of polymer systems depend not only on their composition and structure, but also on environmental conditions such as outside temperature and observation time and the degree of damage, i.e. the internal stress of the material continues to release over time at a certain temperature and finally reaches equilibrium, so it is also known as "creep" response. When the coating is molded, above the glass transition temperature (Tg) of the polymer system, the self-healing caused by this creep response can be observed after a certain period of time, and the relationship between the stress relaxation model E and temperature T and time t is shown in the following patterns:
ρ and ρo are the density of temperature T and reference temperature To polymer, respectively, and alpha T is the displacement factor of the polymer in T. In addition, from the polymer system's viscosity elasticity or creep reply, the crosslink of the coating has a significant impact and reduce its repair performance, and the introduction of fluid repair reagents in the system, can be reflow and greatly increase its creep response effect, so that it restores the original membrane performance.
3.1 Observation and characteristics of self-healing performance
Figure 1 shows two different formulations of self-healing UV coatings after spraying, drying, photo-curing into film SEM morphology, from which they can be seen to have better film-forming properties, in the 103nm amplitude can be observed in the macro-flat solid-state membrane form, but the surface can still see fine bumps. If observed with AFM, when the resolution reaches the nanoscale, the particle shape of the surface micro-convex can be observed, As shown in Figure 2 (sample B), which should be caused by microphedrine separation during film formation. The paint conditions are about the same for different formulations.
3.2 Effect of additive dosage on self-healing performance
After the coating is cured, the membrane surface is scratched with a sharp metal device and then placed at different times to observe the self-healing state. As can be seen from the AFM image of the sample membrane, after a few hours of silence, the scratches have shown partial thinner and lighter, as shown in Figure 3. In the two comparative samples, sample B added more small molecular additives, showing that the repair of scratches at the same temperature than the amount of additives less A, faster and better repair, that is, the additive not only reduces the Tg of the membrane, but also increases its elastic relaxation modus, is conducive to the deformation of the membrane and leveling. Of course, the amount of additives also has certain limits to ensure the aesthetic properties of the membrane as a principle.
3.3 Temperature on self-healing performance
As mentioned earlier, temperature has an important effect on the creep response of polymers, i.e. self-healing, in general, above Tg of the system, as the temperature increases, the molecular motor capacity increases, which is conducive to increasing the relaxation modality E, so that creep response, that is, the self-healing speed and repair effect in the same time have been improved. This work at room temperature to 40oC to compare the same coating film self-healing effect, the results show that with the temperature increase, the self-healing speed and effect have improved, on the other hand, the temperature is limited to the polymer chemical reaction (crosslinking, dissociation) and material use range to adjust.
04 Conclusion
This paper reports on the preparation, film-forming properties and self-healing of a chemically modified method for UV-cured coatings, and the morphological structure of the membrane and the self-healing phenomenon at different formulations and temperatures are observed by SEM and AFM. Based on the process of polymer creep response, the influence of various factors on self-healing function is discussed, which provides meaningful information for the engineering application of self-healing coatings.
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