1, It is suitable for solvent-based baking paint system, and can greatly reduce the cross-linking temperature of baking paint, and will not have adverse effects on the paint film within the recommended addition amount.
2, It can improve the crosslinking density, increase the hardness and gloss of the paint film, and improve the corrosion resistance, hydrolysis resistance, solvent resistance and mechanical properties of the paint film.
3, It can reduce the production cost, improve the efficiency of painting production, and have good storage stability. The amount of addition is different according to the different systems, generally 0.5%-3% of the total amount, can be added at any stage of production.
Leveling and anti-sagging are opposites. To level out well, low viscosity is required, and low viscosity will lead to more serious sag. Only by adjusting the thixotropy can be compromised to achieve unity of opposites.
Mezger et al.1 used the vibration test method to measure the storage modulus G’and the evanescent modulus G” of the coating, as shown in Figure 19-2. For the viscoelastic coating, the storage modulus G’represents the elastic component, and the evanescent modulus G” represents the viscous component. Immediately after painting, the evanescent modulus G” dominates and the paint is leveled. When the storage modulus G’is equal to the evanescent modulus G”, which is the intersection in the figure, the paint structure returns to a gel state and leveling stops. As shown in the figure, paint 1 has a structural recovery time of 33s, which not only has enough time for leveling, but also prevents sagging; while the structure recovery time of paint 2 is too long, about 54s, that is, the thixotropy is too low, so sagging occurs.
The viscosity change during film formation can be found in the Moon cy equation.
yFp-exp[(KiK2P) /(Ka一d) ](19-3) the system viscosity in the formula;
Viscosity of the external phase, the external phase is composed of water, solvent, ptfe dispersion india surfactant and other liquid or water-soluble additives, about 50mPa·s;
p—volume fraction of internal phase;
K1-——constant, for spherical particles, Ki=2.5;
K2——constant, for spherical particles randomly close packed, Ka=0.64.
Above the minimum film-forming temperature, after the latex paint is applied, with the volatilization of water, the lu value and viscosity increase continuously. When the viscosity rises to 1000 Pa·s, the latex paint reaches its surface dryness. After being completely dried into a film, the viscosity exceeds 10/Pa*s.
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