Measurement and mathematical modeling of drying speed of water-based industrial coatings

0 In recent years,
the state attaches great importance to the environmental problems of people's production and living, the efforts to control environmental pollution have increased year by year. In the coatings industry, various departments and local governments have also issued policies to limit the environmental impact of large traditional solvent-based coatings, the promotion of the use of water-based coatings and other environmentally friendly varieties. One of the important differences between water-based coatings and solvent-based coatings in construction applications is that drying is
slower, and water-based coatings will change significantly with the change of temperature, humidity, wind speed and other factors in dry environment
This change of drying speed has a great influence on the water-based industrial coatings with the requirements of construction rhythm, which requires a scientific method to estimate the drying time of water-based coatings in different construction environments, and provide effective data support guidance for actual construction.
This paper aims at water-based epoxy coatings, water-based acrylic coatings, two common varieties of industrial coatings, under different spray film thickness, temperature, relative humidity and wind speed conditions to test the drying speed, and according to the actual test data, through the Lagarrange interpolation method for drying time mathematical modeling, the drying time ti and temperature T, humidity W, wind speed S relationship.1 Experimental part
1.1 Experimental raw materials and equipment
1.1.1 experimental equipment (see Table 1)
1.1.2 substrate
This experiment uses a blasting steel plate with a substrate of 500 mm ×500 mm×2 mm, as shown in Figure 1.
1.2 Experimental Method
First put the fan into the thermostat, adjust the wind speed required for the experiment, and adjust the constant temperature thermostat to a certain temperature and humidity. After the wind speed, temperature and humidity are stable, the water-based paint main agent and curing agent that need to be tested will be mixed evenly, and diluted to the construction viscosity according to the construction guidance, the blasting plate is constructed using airless spray, the steel plate is put into the thermostat and humidity tank immediately after the spray is done, the time is started and the coating drying situation is observed, and the drying time is recorded. Review the thickness of the coating film after the coating film is completely dry. Figure 2 shows a photo of the blasting plate placed in a constant temperature and humidity box.
2 Test Results
2.1 Drying Speed Test of Water-based Epoxy Coatings
According to the above experimental method, the drying speed of grey water-based epoxy coatings was tested, and the test results were shown in Table 3.
2.2 Drying speed test for water-based acrylic coatings
In accordance with the above experimental method, the drying speed of brown water-based acrylic coatings is tested, and the test results are shown in Table 4.
3 Experimental data analysis
3.1 Mathematical modeling of the drying speed of gray water-based epoxy coatings
The value method mathematically models the drying time, and concludes the relationship between drying time ti and temperature T, humidity W, and wind speed S, and the calculation process is as follows:
first investigates the drying time ti with humidity W as the variable when the temperature is T is 10 degrees C and the wind speed is S is 0 m/s.
the correspondence between humidity W and drying time ti is actually measured, such as Table 5.
result, the table dry time ti and the Lagrange interpolation function of humidity W have a slope of K: K: at T-10 degrees C, wind speed S-0 m/s,
The
Lagrange interpolation function of table dry time ti and humidity W is :
the Lagrange interpolation function of the table dry
time ti and humidity W is:
ti, 6W, at the same temperature of 10 degrees C, wind speed S, 1 m/s. The
lagrange interpolation function for the table dry time ti and humidity W is:
ti, 6W, 747.5
the same time, at 885
10 degrees C, wind speed S, 2 m/s
The Lagrange interpolation functions for table dry time ti and humidity W at 10 degrees C, wind speed S=3 m/s are:
ti=7W=492.5
according to the analysis of 4 sets of functions, the difference is shown in Table 8.
Because of its third-order differential 0.65 and interpolation 0.63 approximation, it can be considered that the subsequent slope change of the third-order differential is 0.65, that is, the wind speed S≥3 m/s change in the contribution to the drying speed is about constant, so its 10 degrees C, drying time function slope coefficient modified to:
At S-0, K-11
S-1, K-6-11×0.55
S≥2, K-11×0.552× For × 1.8(1.8-0.65) S-2 to 6× (1.8-0.65) S-2
for the function suffix coefficient, see Table 9.
its first-order differential weighted average is 0.69, so the coefficient correction value: 1 560×0.69S
So, at T-10 degrees C, its drying time ti function is:
S-0, ti-11W-1 560
S At the time of 1st, ti=6W+885
S≥2, ti=6×1.15S-2W=1 560×0.69S
calculates the effect of temperature T on drying time ti, using S=0 m/s as the basis, e.g. Table 10.
from Table 10 to Table 13, we can see that the drying time ti changes with the temperature, the law of change is shown in Table 14.
its variation curve slope of K' (1,819.1-2 006.6)/(30-20)=-18.75, the physical significance lies in the ratio of the drying time difference between any two temperatures to the temperature difference of approximately -18.75. It can be seen that according to the interpolation method, the approximate curve equation of temperature T and drying time ti is as:
ti'-18.75T'2 381.6
extraterred ti' 0, T-127 degrees C, because the above-mentioned drying speed function is based on T-10 degrees C Therefore, the drying temperature ti adjustment coefficient is:
ti/ti10 degrees C (127-T)/(127-10)
so S-0, ti=(11W-1 560) (127-T)/117
at s1, ti is (6W-885) (127-T)/117
S≥2, ti is (6×1.15S-2W-1 560×0.69S) (1 27-T)/117
3.2 Mathematical modeling calculation of the drying speed of water-based acrylic coatings
the same can be introduced water-based acrylic coating drying time ti equation:
S-0, ti-(15.625W-903.75). (178.2-T)/168.2
S=1, ti=(14.375W-406.25)(178.2-T)/168.1 2
S≥2, ti. . . . . . . . . . . . . . .×× . . . . . . . . . . . . . . . . . . . . . . . .× . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74S-766(178.2-T)/168.2 4 Conclusion
From the above experimental results and data analysis, different temperature, wind speed, humidity and film thickness can be derived from the water-based epoxy coating, water-based propylene According to the above results, the preliminary conclusion is as follows:
(1) keep the temperature and humidity unchanged
, with the increase of wind speed, the drying speed accelerates;
(3) keep the humidity and wind speed unchanged, with the decrease of temperature, the drying speed slows down;
(4) with the increase of film thickness, the drying speed slows down.
at the same time, the drying time of water-based epoxy coatings and water-based acrylic coatings used in this experiment in different construction environments can be calculated by the final formula to provide data support and guidance for the actual construction.