Study on the water-based non-stick coating spraying process of PTFE on aluminum baking trays

Fluorine PTFE water-resistant coatings have excellent non-stick properties and excellent stability. In recent years, the market demand for baking trays is increasing, but the existing production process sprayed baking trays prone to cracks and coating shedding phenomenon. This test selects the four factors of the bottom thickness, surface thickness, curing temperature and curing time as the research object, and selects three levels for each factor to test, so as to determine the best process conditions for the production of non-stick inner coating baking traysChina.
1 test
1.1 sample and non-stick coating selection
the test sample used in this test is 375mm×270mm×70mm aluminum baking tray.
1.2 Selection of internal coating process parameters
This test selects four factors: base thickness, surface thickness, curing temperature and curing time as the research object, and selects three levels for each factor. Factor - The horizontal table is shown in Table 1, and the pilot scheme is shown in Table 2.
1.3 detection
1.3.1 roughness
roughness Ra within 2 m to 3 m.
1.3.2 bottom thickness surface thickness
the thickness gauge is used to measure different parts of the inner surface of the baking tray 5 times, taking an average.
1.3.3 coating cracks
the surface quality of the coating is checked under a 10x microscope, requiring a uniform, smooth and crack-free coating.
1.3.4 Coating and aluminum substrate adhesion
Soak the sprayed baking tray in boiling water for 15 minutes, remove it to room temperature and dry it, scratch the surface of the sprayed baking tray with a knife and special plate to obtain 100 small squares. Use nail press tape to quickly remove the tape at a 90O angle to see if the tape sticks the coating down and determine the bonding capacity of the coating to the metal surface.
2 Test and Results Analysis
2.1 Preparation before the spray test
turns the coated barrel for 30 minutes and filters it through a 100-purpose screen. The spray gun and substrate are from 200mm to 300mm and the pressure is from 0.15 MPa to 0.25 MPa.
2.2 Determination of process parameters
This experiment uses orthosectance design, according to Table 2 test scheme, non-stick coating spray process parameters orthosectable test results as shown in Table 3.
from Table 3, the 6th test has a good effect and the lowest score, and the condition A3B2C1D2 is the better scheme. Process parameters: the bottom thickness of 10 m, surface thickness of 15 m, curing temperature of 390 degrees C, curing time of 5min.
the K and R values of each column, A3B1 C1D2 is the optimal scheme. Process parameters: the bottom thickness of 10 m, the thickness of the surface layer 12m, curing temperature of 390 degrees C, curing time 5min.
further validation experiments were carried out on the better scheme and the optimal scheme, and the results were: the optimal scheme (A3B1 C1D2) and the better scheme (A3B2C1D2).
2.3 Test Results Analysis
The baking tray is sprayed according to the most scoring scheme (A2B2C3D3) and the optimal scheme A3B1C1D2 process conditions for calculating K values and R worth it, as shown in Figure 1 and Figure 2 for the low-fold tissue of the non-stick coating.
1 shows that the coating cracks are more, the crack is more serious. Process conditions: the bottom thickness of 14 m, the thickness of the surface 15 m, curing temperature of 400 degrees C, curing time of 7 minutes. The coating in Figure 2 is flat and smooth, with no cracks in the coating. Process conditions: the bottom thickness of 10 m, the thickness of the surface 12 m, curing temperature of 390 degrees C, curing time of 5 minutes. According to table 3 in the most scoring scheme and calculation K is worth the least score of the optimal scheme process conditions for the baking tray spraying, spraying after the baking tray scratch test, Figure 3, the most scoring scheme after the scratch test there is non-stick coating off, and many shedding, area inequality, indicating scratch failure. Figure 4 The optimal scheme did not see the non-stick coating fall off after the scratch test, indicating that the coating and aluminum substate bonded firmly, the coating and aluminum substate adhesion is strong.
the above test results, the best production process parameters for baking trays are 10 m for the base thickness, 12 m for the surface thickness, 390 oC for curing temperature and 5 minutes for curing time.
3 Discuss the effect of
3.1 base thickness, surface thickness
If the bottom layer sprays thick, the bottom solvent evaporates slowly and does not wave completely during the underlying drying process, and the solvent gradually penetrates into the surface coating during the coating curing process in the baking tray to produce cracks. If the bottom spray is thin, because the underlying components are mainly binders, although the coating does not produce cracks, but the adhesion drops, the coating is easy to fall off. If the surface is sprayed thick, the viscosity of the non-stick coating is relatively increased, resulting in poor leveling of the coating, resulting in cracks in the coating. If the surface is sprayed thin, the coating does not produce cracks, but the coating does not stick to decrease.
3.2 Curing temperature impact
curing temperature is high, first, the surface coating quickly drying, resulting in uneven distribution of stress within the coating, easy to produce cracks, while the coating aging white easy to fall off. However, the curing temperature is too low, although it is not easy to produce cracks, the coating can not be fully melted and leveled, so that the coating yellowing soft, the hardness of the coating is reduced, the coating is easy to fall off.
3.3 Effect of curing time
The short curing time indicates that the sprayed baking tray passes through the curing furnace quickly, the coating melts inadequately, resulting in poor binding force between coatings, and the coating is easy to crack and fall off. The curing time is long, the coating is overcoated, the coating is aging and the gloss is easy to fall off and cracks are produced. The curing time in the best solution based on the test results is 5 minutes, and after trial and error, it is concluded that the curing furnace chain speed is the most reasonable at 550mm/min.
4 Conclusion
According to the best process parameters obtained from the test combined with the actual production, the best process parameters of the current production are:
bottom thickness 10 m to 12 m
surface thickness 12 m to 15 m

the curing temperature is 385 to 390 degrees C
the curing time is 4 to 5 minutes
the curing furnace chain speed V is 550mm/min