Polyester/TGIC powder coating curing dynamics analysis.

Abstract: Analysis of the changes of the structure before and after curing of EWA1113 and PWA1221 polyester/TGIC powder coatings by Fourier Transform infrared spectroscopy (FT-IR) to determine whether the powder coating has a curing reaction, and the curing process of powder coatings using differential scanning thermal analysis (DSC) is used to explore the effects of different pigments on the curing behavior of powder coatings. The results showed that the theoretical curing temperature range of EWA1113 and PWA1221 powder coatings was 133.2 to 232.2 degrees C and 151.6 to 232.2 degrees C respectively. Beta extraterrion determines the curing process parameters of EWA1113 powder, linear fitting can obtain gelding temperature T0 of 97 degrees C, curing temperature of TP of 159.6 degrees C, after treatment temperature of Tf of 195. 98 degrees C; the active energy of the reaction is studied by Kissinger and Doyle-Ozawa equation; the active energy Ea is 92.14kJ/mol is calculated by calculation and analysis; and the Crane empirical equation is used for calculation The curing reaction series n is 0.93, and through DSC analysis of the curing characteristics of the coating, the relationship between curing degree and temperature, the theoretical minimum curing time, etc., the conclusion is drawn that the slower the heating rate, the greater the curing degree of the powder coating.
Foreword
The curing film process of powder coatings is divided into three stages, namely, melting, flowing and curing cross-linking, which plays a decisive role in the decorative properties of coatings and the performance of

. In the process of coating curing into film, in order to determine the optimal curing temperature, a large number of experiments are required, the time and cost are larger. The actual curing process depends on the curing temperature and time, and the degree of crosslinking of curing will affect the surface shape, hardness, impact resistance and adhesion of the coating film.
differential scanning thermal method (DSC) technology is widely used in the study of the dynamics of chemical reactions, and experience shows that the method is very effective in analyzing the curing process of thermostate powder coating and studying curing behavior, and can determine curing conditions accurately and quickly. Dynamic analysis in this way is based on measuring the rate at which heat is generated by heat release from chemical reactions, i.e. assuming that the heat generated by chemical reactions is directly related to the degree of reaction, measurements are made at isothermal or non-ethothermal conditions to obtain dynamic parameters. The technology is developing rapidly and is widely used in the coatings industry because of its low sample size and high accuracy of measurements, and is suitable for a variety of curing systems.
This paper analyzes the change of the structure before and after the curing of powder coating by infrared analysis, analyzes the curing process of powder coating by using differential scanning amount heat meter, studies the active energy Ea of reaction by Kissinger differential method and Doyle-Ozawa equation, calculates the curing reaction series n by using crane empirical equation, discusses its curing dynamics, lays a theoretical foundation for actual production, and can effectively save energy and time.
experimental part
1.1 Raw materials and instruments
polyester/TGIC powder coatings: EWA1113, PWA1221, Zibo Yuyu New Materials Technology Co., Ltd.
electrostitive sprayer: HY-301, Yi tu coating machinery and equipment Co., Ltd.; vacuum drying box: DZF-6050, Shanghai Yiheng Scientific Instruments Co., Ltd.; Infrared spectrometer: Avatar-360, Thermo-Nicolet Corporation of the United States; differential scanning heat meter: 204F1, NETSCHZ, Germany.
1.2 Test and Symptom
1.2.1 Infrared Spectroscopy (FT-IR) Analysis
uses an infrared spectrometer for red appearance, with samples mixed with KBr pressure sheets with wave numbers ranging from 450 to 4000cm-1.
1.2.2 DSC test
using a differential scanning amount heat meter, in the program temperature control, the measurement of the product's glass transition temperature (Tg), the rate of warming is 5 degrees C/min, 10 degrees C/min, 15 degrees C/min, 20 degrees C/min, the environment is N2 atmosphere, the heating range is 25 to 300 degrees C.
models of curing dynamics of thermostate resins are 3 kinds, n-order models, Kamal models and self-catalytic models, which are widely used because the n-order model does not involve chemical matching in the system, and the expression is simple and effective. The n-order model expression is shown in the pattern (1).
, alpha-curing degree, T-curing temperature, t-curing time.
according to dynamic model (1), the relationship between curing degree and curing time at different heating rates and the curing degree and temperature of powder coatings with different pigments can be obtained.
results and discussion
2.1 Infrared Spectroscopy (FT-IR) Analysis
Figure 1 shows the infrared spectrum before and after the curing of EWA1113 powder coating.
can be seen from the infrared curve before the curing of the System in Figure 1, 3426cm-1 is the telescopic vibration peak of the OH key, at 2964cm-1 is the telescopic vibration peak of the C-H key, at 1721cm-1 is the telescopic vibration peak of the C-O cluster, and at 1407cm-1 it is the N-CH2 and TGIC hybrid ring. Absorption peak of N atom and C atom, 1461cm-1, 1375cm-1 is the symmetrical deformation peak of CH3 and -CH2, at 1265cm-1 is the telescopic peak of C-O in COOH; The peak structure shown in the infrared spectrum is consistent with the polyester resin/TGIC architecture. It can be seen from the infrared spectrum after system curing that the telescopic vibration peak of the OH key still exists at 3426cm-1, and the peak of C-O at 1721cm-1 is moved to 1631cm-1 and decreased significantly. The C-O peak at 1265cm-1 is moved to 1261cm-1 and the intensity is weakened, mainly because the - COOH group participates in the curing reaction, and the resulting - COOC - causes the change in peak displacement.
2.2 DSC Curve Analysis
2.2.1 Powder coatings of different pigment types
five 2 is the DSC curve (warming rate of 15 degrees C/min) before the curing of EWA1113 (pure white) powder coatings and PWA1221 (green and white) powder coatings, and explores the effects of 2 pigments on the curing behavior of powder coatings.
as can be seen from Figure 2, there is a significant heat absorption change in both powder coatings, where the temperature is the melting point of the powder coating, which occurs at 56.1 degrees C and 57.8 degrees C, respectively, and the temperatures of the two are close. When the temperature rises further, there is a small change in the curve, indicating that at this temperature the powder begins to cure, the EWA1113 powder coating begins to cure at a temperature of 133.2 degrees C and the PWA1221 powder coating is 151.6 degrees C; The heat release rate is at 184 degrees C and 186 degrees C respectively, which is also the fastest temperature of powder coating curing, and then continue to raise the temperature, the curve slowly slides, the heating reaction enters the end, EWA1113 and PWA1221 powder temperature is 232.2 degrees C, the curing also ends, that is, curing completely. It can be seen that the type of pigment does not have a significant effect on the curing temperature, because the pigment is not directly involved in the curing reaction, but indirectly affects the fusion of the components of the whole system. By analyzing the DSC curve of 2 powder coatings, it can be concluded that the curing temperature range of powder coatings is 133.2 to 232.2 degrees C and 151.6 to 232.2 degrees C, respectively.
the curing reaction of powder coatings is also related to the pigment type of powder coatings, and different pigments also have an effect on curing degree. Figure 3 shows the effect of different pigments on the curing degree of powder coatings.
From Figure 3, it can be seen that the curing degree of powder coatings with different pigments is consistent with the trend of temperature change, at about 180 degrees C, the curing degree rises the fastest and the curing reaction is the fastest;
temperature DSC curves of polyester powder coatings with different pigment types are shown in Tables 1 and 4.
From Table 1 and Figure 4, it can be seen that the trend of the DSC curve is consistent at different heating rates, the rate of warming increases from 5 degrees C/min to 20 degrees C/min, the initial curing temperature, peak temperature, curing termination temperature and heat release peak position of the system are all moving in the direction of high temperature, pigments have little effect on the trend of curing reaction. The reason for moving to high temperature is because the heating rate is accelerated, dH/dt (thermal efficiency generated per unit of time) is increased, thermal inertia is increased, the resulting temperature difference is also increased, so the heating peak moves to the high temperature.
of the curing process parameters of 2.2.2
the determination of the curing process parameters is generally based on T-beta extraterrion. As can be seen from Figure 4, the DSC curve of different heating rates has different temperature heating peaks, but in actual production, it is often thermostat curing, so extraterrorization is used to reduce this error, to obtain the temperature at beta-0, and then to obtain the optimal curing temperature range.
Based on the data in Table 1, EWA1113 powder coating is used as an example to map the warming rate beta with T (starting temperature T0, peak temperature TP and termination temperature Tf) and to fit it linearly, extratrolly to beta-0, as shown in Figure 5.
can be seen from Figure 5, linear fitting results in a gelding temperature of T0 to 97 degrees C, a curing temperature of Tp to 159.6 degrees C, and a post-treatment temperature of Tf to 195.98 degrees C. They reflect the curing characteristics of the system. However, due to the complexity of the curing process in actual production, the T0 and Tp obtained by fitting cannot be directly used for the actual production curing temperature, usually in order to improve the curing efficiency and reduce the curing time, the curing temperature at the time of production is higher than the theoretical temperature.
2.2.3 Curing reaction dynamics parameter
(1) active energy Ea
obtains the DSC curve data of EWA1113 polyester powder coating from Figure 4 as shown in Table 2.
dynamics parameters are usually determined by obtaining DSC curve data using the Kissinger necation method and the Doyle-Ozawa equation. Their rationale is to think of the DSC curve at the top of the heat release peak as the maximum rate at which the curing reaction occurs, assuming that the reaction series n does not change during the reaction.
Kissinger's nediable equation is shown in equation (2).
Doyle-Ozawa equation is shown in equation (3).
, beta-warming rate, K/min; Tp-peak temperature, c; Ea-oscic active energy, kJ/mol; R-molar gas constant, 8.314J/(mol.
1/Tp distribution of -ln (beta/Tp2) and ln beta is shown in Figure 6, based on test data from table 2. ln (beta/Tp2)-1/Tp linear regression linear equation: y-28.641 plus 11.869x, ln beta-1/Tp linear The straight-line equation of regression: y-14.442-10.969x, the system's oscically active energy Ea is calculated to be 92.14kJ/mol.
(2) reaction series
where n is the reaction series. Using -ln beta to 1/Tp, linear regression can be used to arrive at the curing reaction series n-0.93.
2.2.4 Curing characteristics
(1) Curing degree and temperature
powder coating curing and reaction heating rate also have a relationship, heating rate will have an impact on curing degree, Figure 7 shows the powder coating at different heating rate curing degree and temperature relationship.
From Figure 7, it can be known that the slower the heating rate, the greater the curing degree of the system, the faster the temperature of the system at the same curing degree, the higher the temperature of the system, indicating that the slower the rate of warming, the lower the curing temperature required for the curing reaction.
(2) theoretical curing time
powder coating can determine the curing time change at different temperatures through the iso-temperature DSC test, can determine the minimum curing time. The iso-temperature DSC curve data tested is shown in Table 3.
can be seen from Table 3, the higher the curing temperature of EWA1113 and PWA1221 powder coatings, the shorter the curing time. It is shown that as the temperature increases, the curing reaction rate will accelerate, but it is not unlimited heating, but also consider the stability and gloss of the coating.
Conclusion
(1) Analysis of changes in the structure before and after curing of powder coatings by Fourier transform infrared spectroscopy, the infrared map can be used to determine whether the coating is cured completely; The effects of different pigments on the curing behavior of powder coatings are derived, and the theoretical curing range of powder coatings is 133.2 to 232.2 degrees C and 151.6 to 232.2 degrees C, respectively.
(2) using T-beta extraterrion method to determine the curing process parameters of EWA1113 powder, linear fitting can obtain the gelding temperature T0 to 97 degrees C, the curing temperature TP to 159.6 degrees C, the after-treatment temperature Tf to 195.98 degrees C.
(3) By studying the active energy of the reaction by Kissinger nexus method and Doyle-Ozawa equation, the active energy Ea is calculated by calculation and analysis, and the curing reaction series n-0.93 is calculated using the Crane empirical equation to explore its curing dynamics.
(4) Through DSC analysis of the curing characteristics of the coating, the relationship between curing degree and temperature, theoretical minimum curing time, etc., to arrive at the same curing degree, the slower the rate of warming, the lower the temperature of the system, the lower the curing temperature required by the curing reaction.
this paper has laid a theoretical foundation for the curing of polyester powder coatings in actual production, which can effectively save energy and time.
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