Abstract: a kind of resin was selected to prepare powder of different formula by changing the composition of filler in powder formula and adding different antioxidants. The final color difference was measured by traditional electric baking and gas oven baking, so as to find out the factors affecting the yellowing performance of powder system.
1, introduction
Powder coating is a new type of coating. Compared with traditional liquid coating, powder coating is a kind of 100% solid powder coating without solvent. It has the characteristics of no solvent, no pollution, recyclable, environmental protection, energy and resource saving, labor intensity reduction and mechanical strength of coating film, etc.
The product does not contain toxicity, solvents and volatile toxic substances, so there is no poisoning, fire, discharge of "three wastes" and other public hazards, and it fully meets the requirements of national environmental protection law.
Compared with the liquid coating, the powder coating is convenient for transportation and storage. The common coating contains about 20-50% water or solvent, while the powder coating has neither water nor solvent, which is completely solid, so the transportation is convenient and safe.
In addition, when the temperature of transportation and storage is lower than 0 ℃, the coating with water or solvent will often freeze, and the powder coating does not have this problem. Furthermore, the application of powder coating is developing rapidly, and the application field is becoming wider and wider.
However, compared with the liquid coating, the coating of powder coating needs to be baked to make the base resin cross-linked with the curing agent. Most of the baking of powder coating is done by electric oven.
However, in some regions or countries, the gas supply is simple, so in these regions or countries, the dryers are more inclined to use gas furnace for powder coating baking.
Compared with electric baking, due to the presence of nitrogen oxides in the baking process of gas furnace, the coating of powder coating has serious yellowing after curing, which brings a lot of trouble to the sprayer. Because there are many areas using natural gas for baking, it is very important to improve and solve this problem.
2. Experiment
2.1 experimental instruments and materials
Tse-32 twin screw extruder, electronic scale, binder oven, Q-Lab spray plate, spray gun, clean plastic bag, barium sulfate, titanium dioxide, leveling agent, polyester resin, 701, benzoin, TGIC, colorimeter, electric oven, gas oven, coffee mill.
2.2 experimental method
In this experiment, the color difference between electric heating oven baking and gas oven baking was compared by changing the material composition in powder formula, adding different kinds of antioxidant and changing the amount of antioxidant.
According to the following experimental formula, weigh the material, place the weighed material in a clean plastic bag, mix and shake it well, and extrude the film with an extruder. Grind and pulverize the tablet with coffee mill, and spray it on two spray plates with spray gun.
Put the two spray plates in binder oven and gas oven respectively, and bake in electric oven and gas oven respectively under the conditions of 200 ℃ / 10min, 200 ℃ / 20min and 200 ℃ / 30min.
After baking, take out the spray plate, cool it, take the spray plate of electric heating baking 200 ℃ / 10min as the standard plate, and measure the color difference in turn with the color difference meter.
2.3 test steps
According to the above experimental formula, after spraying, the powder is placed in the binder oven and the gas furnace respectively at 200 ℃ / 10min, 200 ℃ / 20min and 200 ℃ / 30min for traditional electric baking and gas furnace baking. Measurement of chromatic aberration
It can be seen from the above experimental results that: if the baking time is prolonged, the electric baking coating will also turn yellow. If the gas furnace is used for baking, the coating will turn yellow seriously. This kind of yellow coating is difficult to be accepted in the actual spraying process, so the problem of coating turning yellow must be solved when the gas furnace is used for baking. In view of the above problems, antioxidant is added to the powder formula to improve the yellowing resistance of the powder coating.
It can be seen from the above data that adding antioxidant 1 can effectively reduce the yellowing degree of powder coating gas furnace baking. Increase the amount of antioxidant 1
The results show that the color difference between gas furnace baking and electric baking is further reduced when the amount of antioxidant is increased from 1 ‰ to 2 ‰. Continue to increase the amount of antioxidant 1
The experimental data show that when the amount of antioxidant 1 is increased from 2 ‰ to 3 ‰, the color difference between gas furnace baking and electric baking is not much reduced. Select another antioxidant 2 for the same experiment
Therefore, antioxidant 2 can also improve the yellowing resistance of powder coatings. Increase the amount of antioxidant 2
It can be seen from the above experimental results that when the amount of antioxidant 2 is increased from 1 ‰ to 2 ‰, the color difference between gas furnace baking and electric baking of powder coating is not significantly reduced. Therefore, for antioxidant 2, when the dosage is 1 ‰, it reaches the saturation state. Add antioxidant 3 to the same powder formula
The experimental results show that the addition of antioxidant 3 does not improve the yellowing problem of powder coating gas furnace, but reduces the yellowing resistance of the whole powder system, but reduces the color difference of electric baking. Increase the amount of antioxidant 3
It can be seen from the experimental data that the color difference value does not decrease but increases when the amount of antioxidant 3 is increased, which indicates that antioxidant 3 does not play a positive role in improving the yellowing resistance of gas furnace of powder coating, and it is not suitable for improving the yellowing resistance of gas furnace of powder coating. Select special resin suitable for gas furnace baking for experiment
It can be seen from the experimental data that the color difference between gas oven baking and electric baking of powder system is obviously reduced when the special resin suitable for gas oven baking is selected as the base resin.
3. Discussion on experimental results
According to the value of de measured by the above experiments, the yellowing resistance of gas furnace of powder system is directly related to the powder formula. The yellowing resistance of powder coating can be improved by adding appropriate antioxidant, but when the amount of added reaches a certain value, it will reach saturation state, and no significant improvement on the yellowing resistance can be achieved by adding it.
Some antioxidants which are suitable for improving the yellowing resistance of electric baking are not suitable for improving the yellowing resistance of gas furnace of powder system; selecting special resin which is suitable for gas furnace as the base material will also improve the yellowing resistance of powder system. Source: Anhui Shenjian New Material Co., Ltd
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