A comparative study of the aging properties of TGIC and HAA powder coatings

Abstract:
At present, the systematic comparison study of TGIC and HAA two kinds of outdoor curing agent coating performance is relatively small, the study uses boiling, baking, solvent wipe and artificial accelerated aging and other methods to experiment with different curing agent coatings, the results show that: TGIC and HA are used respectively When A cures the same polyester, the polyester-TGIC coating has better water resistance and yellowing resistance under high temperature baking than the polyester-HAA coating, and the polyester-HAA coating has better solvent wipe and weather resistance than the polyester-TGIC coating.
thermoosteroid powder coating as a polymer material, its properties mainly depend on the structure and aggregation state of the substitin resin used, and curing agents play a key role in its aggregation state.
isocyanate triglycerides (TGIC) and hydroxyamide (HAA) are the two mainstream curing agents of outdoor thermoosterone powder coatings, powder coatings using TGIC as curing agents can usually obtain excellent light, thermal stability, wear resistance and excellent weather resistance, so since the advent of TGIC, has been favored
China
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However, with the increasing demands on people's lives and environmental awareness, TGIC because of its inherent toxicity and environmental damage in the manufacturing process, Europe and Australia banned the use of TGIC in 1998, China's Ministry of Industry and Information Technology in 2010 TGIC in the obsolete product catalog; HAA, as the most ideal alternative to TGIC, has developed rapidly in the industry since its successful development, and in 2003 officially replaced TGIC as the world's largest weather-resistant powder coating curing agent.
coating with HAA as a curing agent is not inferior to TGIC powder coating in individual performance, but the comprehensive performance is no less than TGIC powder coating. At present, TGIC powder coating also occupies a large share, in addition to HAA has individual weaknesses, mainly due to the lack of understanding of HAA powder coating performance, habitually extended TGIC powder coating, so this paper from the outdoor powder coating aging performance, respectively, using TGIC and HAA preparation powder coating, compared with the study of TGIC and HAA powder coating in aging performance of their respective advantages and disadvantages.
1, experimental part
1.1 experimental raw materials
ultra-weather-resistant polyester resin (referred to below referred to as polyester); curing agent TGIC; curing agent HAA; titanium white powder; sulphate; leveling agent; sabbath fragrance; lightener.
1.2 powder coating preparationAccording to the basic formula of Table 1 to prepare powder coating, the process is: ingredients →mixed→ extruded →pressure→sieve→sieve→ products, the prepared powder coating with electrostectrectectrectrecturization spray, and then cured under 200 degrees C / 10min conditions to obtain a powder coating.1.3 Experimental test and conditions
1.3.1 and other temperature curing tests
using differential scanning amount heat meter (DSC) for the powder coating isothermal curing test, the test conditions are: N2 as a protective gas, flow 50mL/min;
1.3.2 boiling test
boiled in a sterilized pressure cooker with deionized water at a temperature of 120 degrees C. After the boiling test is complete, dry the surface moisture of the coating and test the color difference and gloss.
1.3.3 Absorbent Rate Experiment
Calculating the suction rate of the coating using the poor quality before and after absorbent, the quality of the coating after vacuum drying is recorded as m1, the quality of the coating is recorded as m2 after water immersion or boiling with paper, and the water absorption rate is 100% after the surface of the coating is × dried with paper.
1.3.4 Baking test
is heated and baked in a blow-style oven at a time of 2h. After baking, test the color difference and gloss of the coating.
1.3.5 solvent wipe test
powder coating sprayed on aluminum substrate, 200 degrees C/10min curing, the use of butyl ketone for instrument wipe experiments, test plate load 1000g, wipe frequency 50 times / min. Wipe the coating to the bottom of the dew, record the number of wipes, wipe the coating 3 times per thickness, and average the results of the three wipes.
1.3.6 Artificial Accelerated Aging Test
Using QUV-313 for artificial accelerated aging test, the test conditions are: irradiance 0.71W/m2, 60 degrees C light 4h, 50 degrees C condensation 4h. After the experiment is completed, the color difference and gloss of the coating surface are tested.
1.3.7 coating thickness test
be carried out in accordance with GB/T 4957.
1.3.8 coating gloss test
be performed according to GB/T 9754, using a 60-degree shot angle determination.
1.3.9 coating chromic
test is carried out in accordance with GB/T 11186.2, 11186.3.
2, results and discussion
2.1 iso-temperature curing test
fgication 1 shows the process curve of iso-temperature curing at 200 degrees C for polyester-TGIC and polyester-HAA, respectively. results show that the maximum reaction rate of polyester-TGIC and TGIC during temperature curing is 21s, and the maximum reaction rate of polyester-HAA is 15s, which means that polyester and TGIC react faster, and the degree of curing reaction curve (Figure 2) shows that at 600s, polyester and TGIC react 98.82%, while polyester and HAA react at 94.60%.
At 200 degrees C, polyester and TGIC react faster and more responsively than polyester and HAA at the same time, possibly because polyester contains a curing promoter that accelerates the reaction between polyester and TGIC, which has no significant acceleration effect on polyester and HAA reaction. Overall, the degree of reaction between polyester and TGIC and polyester and HAA was not significant under the condition of curing at 200 degrees C/10min, and the effect on the overall performance of the coating was small. 2.2 Water Resistance Test Figure 3 shows changes in color difference and preservation rates between polyester-TGIC coatings and polyester-HAA coatings at different boiling times.
From Figure 3, it can be seen that as the boiling time increases, the color difference of the coating increases and the preservation rate decreases, and it can also be found that the color difference and preservation rate of the polyester-HAA coating changes more than the polyester-TGIC coating, especially the polyester-HAA coating. The rate drops sharply, and as the boiling time increases, the surface of the polyester-HAA coating is severely lost in light and even powdered, possibly due to the fact that the polyester-HAA coating is freer and larger at 120 degrees C, and the water penetrates more easily into the inside of the coating and reacts with the coating during the boiling process.
, in order to compare the affinity between coating and water, the absorption rate of coating was examined under different conditions. Table 2 is the absorption rate of the coating at room temperature and after boiling 2h at 120 degrees C, it can be seen that at room temperature, the polyester-TGIC coating has a slightly higher water absorption rate than the polyester-HAA coating, and after 2h at 120 degrees C, The water absorption rate of polyester-TGIC coating and polyester-HAA coating has changed greatly from room temperature year-on-year, and the water absorption rate of polyester-HAA has increased sharply after boiling and the water absorption rate is much higher than that of polyester-TGIC coating.
Caused by different conditions of water absorption rate changes, but because the coating at room temperature conditions, the coating structure remains dense, water is more difficult to absorb penetration into the inside of the coating, so the absorption rate of the coating is relatively small, however, under 120 degrees C boiling conditions, the structure of the coating itself has changed dramatically, a large amount of water into the inside of the coating led to a sharp rise in the absorption rate.
For polymers, usually below the glass transition temperature, its internal structure is presented as a rigid "hole", above the glass transition temperature, its internal structure is presented as a flexible "free volume", polyester-TGIC coating and polyester The different water absorption rates of the -HAA coating at 120 degrees C may be due to the fact that the polyester-HAA coating is more flexible than the polyester-TGIC coating, which has a large free body volume at 120 degrees C, allowing it to wrap more water. 2.3 Temperature Resistance Test Figure 4 shows changes in color aeration and preservation rates between polyester-TGIC coatings and polyester-HAA coatings baked at different temperatures. It can be seen that with the increase of baking temperature, the color difference of the coating becomes larger, and the color difference of polyester-HAA coating is much larger than the polyester-TGIC level, mainly due to the nitrogen elements in HAA itself and in the production process with easy color change and nitrogen-containing impurities left in the PRODUCTION process of HAA, a series of reactions will occur at high temperatures to produce some raw color groups leading to yellowing.
During the baking process, the preservation of polyester-TGIC coating remained unchanged first, followed by a sharp decrease in the preservation rate at 250 degrees C, the main coating at 250 degrees C, resulting in a secondary melting phenomenon, resulting in a severe orange peel on the coating plate surface, while the polyester-HAA coating under this test conditions, the preservation rate remained unchanged or slightly increased, mainly due to the reflow of additives on the coating surface.
compared with polyester-TGIC and polyester-HAA coatings at different temperatures, it can be seen that polyester-TGIC's yellow-resistant performance is much better than polyester-HAA, but at 250 degrees C polyester-TGIC coating will appear secondary melting, seriously undermining the normal use of the coating, so polyester-TGIC should also avoid excessive temperature during use. 2.4 Solvent Resistance Test Table 3 is the result of solvent wipes of polyester-TGIC and polyester-HAA coatings at different thicknesses. It can be seen that with the increase of coating thickness, solvent-resistant wipe performance is gradually improved, and when comparing the solvent-resistant wipe performance of polyester-TGIC with polyester-HAA coating, it can be seen that polyester-HAA solvent-resistant wipe performance is better than polyester-TGIC performance. Usually the higher the crosslink density, the better the solvent wipe resistance, resulting in better polyester-HAA wipe resistance than polyester-TGIC, possibly due to the higher cross-link density inside the polyester-HAA coating.
2.5 Human-accelerated Aging Test Figure 5 is the test results of polyester-TGIC and polyester-HAA coatings at different aging times, and it can be seen that as aging time increases, the color difference of polyester-TGIC coatings is gradually increasing, the preservation rate is decreasing gradually, and the color difference of polyester-HAA coatings is gradually increasing. Increased, the preservation rate is gradually decreasing, but also can be found that in the same aging time, polyester-HAA coating color difference and photon preservation rate changes less than polyester-TGIC coating, that is, polyester-HAA coating weather resistance is better than polyester-TGIC coating.
3, Conclusion
(1) when TGIC and HAA cured the same polyester, polyester and TGIC reaction rate is faster than polyester and HAA reaction rate.
(2) polyester-TGIC coating has better water resistance and yellowing resistance under high temperature baking than polyester-HAA coatings.
(3) polyester-HAA coating has better solvent wipe resistance and weather resistance than polyester-TGIC coatings.