Research on Low Temperature Curing Hydrophobic/Graphene Anticorrosive Powder Coating

Abstract:
with epoxy E-12 as the base resin, modified phenols as curing agents, K-7318 as curing promoter, can effectively reduce the curing temperature; The addition of nanoSiO2 and fluorowax modified by 1H, 1H, 2H, 2H-perfluorooctyl triethyl silane can effectively improve hydrophobicity, and the addition of the appropriate amount of graphene can effectively improve corrosion resistance. Through melting extrusion and grinding powder, the low temperature cured ultra-hydrophobic anti-corrosion powder coating was successfully prepared. Through SEM, TEM, neutral salt spray, impact resistance, contact angle testing and other methods to the low temperature curing ultra-hydrophobic anti-corrosion coating performance was characterized and tested, the effects of curing agents and curing promoters on curing temperature were examined, and the effects of modified nanoSiO2, fluorowax and graphene dosage on coating hydrophobicity and corrosion protectionThe results show that the optimized coating has excellent hydrophobic, anti-corrosion and mechanical properties.Introduction
Introduction
Powder coatings because of their solvent-free, low VOC and high utilization advantages, is attracting more and more attention, but its own curing conditions require high temperature and a long time, directly improve the cost of coating, the actual use of higher energy consumption, environmental protection and energy conservation challenges, and in the face of thermal materials to limit the application of powder coatings, such as plastics and wood. Therefore, the market and downstream manufacturers on the low temperature curing requirements are increasingly urgent.
metal products are widely used in life, corrosion has always been a difficult problem. Especially in wet and dark environments, corrosion problems are serious, such as various metal work parts underground. It is reported that corrosion has caused great damage to the national economy and has also polluted the environment. Coatings are now the most reliable and simplest means of protection, the coating to the ultra-hydrophobic function can effectively improve the anti-corrosion effect of the coating, supplemented by anti-corrosion materials, can significantly improve the anti-corrosion performance of powder coatings. The key factors for the formation of ultra-hydrophobicity are high roughness and low surface energy, while the existing method is to rough the surface and then low surface energy, so as to prepare the super-hydrophobic coating. Complementary anti-corrosion materials such as graphene or zinc can significantly improve the corrosion resistance of coatings. Zinc is now the most used anti-corrosion material, and graphene-type materials because of its own properties is one of the most promising anti-corrosion materials today. Epoxy resin has excellent anti-corrosion properties and is widely used in anti-corrosion coatings.
study used epoxy resin as a film, modified phenol as a curing agent, K-7318 as a curing promoter, SA-186 as a rough agent, added by 1H, 1H, 2H, 2H-perfluoroxinski III The nanoSiO2 particles and fluorowax modified by ethylene silane, and added the appropriate amount of graphene, get the surface as hydrophobic, the coating contains graphene anti-corrosion layer of low-temperature cured ultra-hydrophobic anti-corrosion coating, the coating shows excellent hydrophobic, anti-corrosion and mechanical properties.
Experimental Part
1.1 Experimental Raw Materials
1H, 1H, 2H, 2H-Perfluorohexyl Triethylsilane, Waterless Ethanol, Teesilate (TEOS), Ammonia, Tehydrofuran (THF), NaCl: Analysis Level, National Pharmaceutical Group Chemical Reagents Co., Ltd.; -12): Huangshan Jinfeng Industrial Co., Ltd.; Sulphate: Changzhou Fengshuo Chemical Co., Ltd.; Titanium White Powder: Shanghai DuPont Chemical (International) Co., Ltd.; Graphene: Industrial Grade, Sixth Elemental Materials Technology Co., Ltd.; Phenol curing agent, K-7318, SA-186: Six Anjie Tongda Chemical Co., Ltd.; Fluorowax: Changzhou Lingda Chemical Co., Ltd. All of the above are industrial grade.
1.2 Experimental process
1.2.1 Preparation of modified silica
will be waterless ethanol 50mL, ammonia 2mL, TEOS1mL at 40 degrees C, stirring reaction 6h, and then 1H, 1H, 2H, 2 H-perfluorooxine triethyloxysilane (compared to waterless ethanol volume fraction of 0.1%, 0.3%, 0.5%, 0.7%, 0.9%) drops added to the system, reaction 2h, low temperature cooling dry, modified silicon dioxide powder, as shown in Figure 1.
1.2.2 Preparation of modified graphene
graphene powder added to THF high-speed dispersion of 10min, added radon sulfate, stirred evenly, using low temperature cooling drying, powdered material. Add to the shredder, turn 60s, remove, 180 mesh brush points, together with the remains of the screen added to the shredder, 3 consecutive times, that is, to make modified graphene material.
1.2.3 Preparation of low-temperature cured ultra-hydrophobic antiseptic powder coatings
the above-mentioned preparation of modified SiO2, fluorowax and other 55 parts (mass, the same between 15 and 26 phenolic curing agents, 0.1 to 1 k731) 8,0.2 to 1.2 copies SA-186, 2 to 5 servings of titanium dioxide powder, 20 to 30 servings of niobium sulfate, modified graphene and other raw materials stirred well after melting extrusion, grinding powder, oversieve (200 mesh) that is to get low temperature curing ultra-hydrophobic anti-corrosion powder coating.
electrostature spray method, the powder sprayed on the cold-rolled plate, at 130 degrees C, curing 30min, that is, low temperature curing ultra-hydrophobic anti-corrosion coating, paint film thickness of about 60 to 80 m.
1.3 Analysis and testing
using PT-705-B contact angle measuring instrument of Dongguan Pussett Inspection Equipment Co., Ltd. to determine the water contact angle of the coating; Open test equipment Co. , Ltd. precision salt spray test machine, test medium of 5% NaCl aqueous solution, all testing processes are carried out at room temperature (23 x 2) degrees C;
results and discussion
2.1 curing promoter dosage on curing temperature
This curing promoter is reported to achieve 130 degrees C/30min curing, now the curing temperature is set to 130 degrees C, curing time of 30min and other substances dosage unchanged conditions, change the curing promoter dosage, coating test results as shown in Table 1.
as can be known from Table 1, when the curing promoter dosage increases from 0.1% to 0.9%, the adhesion and impact resistance of the coating increase with the increase of the dosage and then a steady trend. When the dosing is less, the coating is not fully cured within 30min, the mechanical properties of the coating are naturally weak, when the dosing is too high, the coating surface is poor, the coating curing is rapid, has not yet leveled, so the coating surface is poor. In summary, the curing promoter dosage was determined to be 0.5% in the following experiments.
2.2 Effect of curing agent dosage on coating performance
To determine the optimal dosage of phenolic curing agents, only the curing agent dosage is changed at a curing temperature of 130 degrees C and the curing time is unchanged at 30min and other substances, and the coating test results are shown in Table 2.
table 2 shows that when the curing agent dosage increases from 15% to 26%, the adhesion and impact resistance of the coating increase with the increase of the dosage and then decrease. When the amount of dosing is less, the coating curing is incomplete, the mechanical properties of the coating will naturally be weak, when the dosing is too high, the crosslink density of the coating is larger, reducing the movement of the molecular chain, thereby reducing the flexibility of the coating, so the impact resistance is reduced. And adhesion test to take the rowing method, in the rowing, because of the curing agent dosage is high, the coating flexibility is lower, the coating edge is more serious, so the adhesion is lower.
is known by Table 2, with the increase in curing agent dosage, the plate surface is first hanging and then good and then orange peel state. When the curing agent dosage is less, the curing rate is low, the melted powder moves down under the action of gravity, which appears as a flow hook on the surface, when the dosage is high, the gel time is short, the coating has not yet leveled or cured, so orange peel appears, the surface of the plate is poor. So in the next experiment, the curing agent dosage was determined to be 21%.
2.3 SA-186 dosing on surface roughness, hydrophobicity and corrosion protection
High roughness is one of the prerequisites for hydrophobics, and the result of this study is a dendritic structure obtained by chemical reaction, thus improving roughness. The coating is now shown in Figure 2 in order to determine the optimal dosage of SA-186, with a curing temperature of 130 degrees C, a curing time of 30min, and a curing agent dosage of 21% and other substances unchanged. The results show that with the increase of dosing, the mastosotic structure formed on the coating surface is on the rise. When the dosing increased from 0.90% to 1.20%, the increase in density of the mastura structure available from Figures 2D and E was not significant. This is also well demonstrated from the water contact angle, with the increase in dosing, hydrophobic angle is on the rise, when the dosing increased from 0.90% to 1.20%, hydrophobic angle did not increase significantly. SA-186 is the acid-modified ring , in high temperature conditions, the high activity of the ring is the first to react with epoxy resin to increase the reaction, the reaction activity of seramine is low, although there is a certain catalytic effect, but its content is not sufficient to completely cure epoxy resin, produce a low polymer crosslink, so that the entire coating forms a microscopic anchor point, reducing the fluidity of the coating. With the increase of temperature, carboxy acid and epoxy react, so that the molecular chain produces a sharp contraction, but because of the presence of anchor point, limiting mobility, coating shrinkage can not be compensated, resulting in uneven lactation structure of the coating, thereby improving surface roughness, to improve hydrophobic and anti-corrosion purposes.
hydrophobicity can improve the corrosion resistance of the coating, so this study uses neutral salt spray to test the anti-corrosion performance. As can be learned from Table 3, with the increase of SA-186 dosing, anti-corrosion performance increases, the increase of mastostic structure, so that water and other corrosive media are not easy to contact with the coating as a whole, directly reducing the possibility of electrochemical and chemical corrosion, and thus improve corrosion resistance. However, from Table 3 also learned that with the increase in SA-186 dosage, the trend of mechanical decline, mainly due to SA-186 dosage is too high, coating shrinkage is too large, flexibility is not enough. Taken together, sa-186 dosing was determined to be 0.90% in the next experiment.
2.4 The preparation of modified silica and its effect on hydrophobic and anti-corrosion
according to 1.2.1 sections, nanoscale SiO2 was prepared and modified with fluosilane, nanoSiO2 nanoparticle results are shown in Figure 3F. The effect of modified nanoSiO2 dosing on coating hydrophobicity was examined.
to further improve roughness, add modified SiO2. In order to determine the optimal dosage of modified SiO2, the curing temperature is set to 130 degrees C, the curing time is 20min, the curing agent dosage is 21%, the SA-186 dosage is 0.9% and other substances dosage is unchanged, only change the amount of modified SiO2, as shown in Figure 3. The results show that with the increase of dosing, the hydrophobic angle is on the rise. When the dosing increased from 0.5% to 1.1%, the upward trend in hydrophobic angles of the available coatings from Figures 3C and E was not obvious. When modified SiO2 is added to the system, in the melting and curing phase, because the fluosilane modified nanoSiO2 is less compatible in the system, it will surface to the surface, on the basis of the milk protrusion to form a sub-rough structure, so that the roughness of the coating surface increased again, thereby improving hydrophobicity, as shown in Figure 4. Compared with the addition of SA-186 only, the formation of secondary rough structure, there is a significant improvement in hydrophobic angle.
is available from Table 4, with the increase of modified SiO2 dosing, the performance of salt spray resistance is increased first and then stable trend, but there is a significant improvement over only adding SA-186. When the amount of addition is less, such as 0.15%, the increase of secondary rough structure is less, the hydrophobic angle is lower, the performance of salt spray resistance is not improved, when the amount of addition is too high, such as from 0.50% to 1.10%, the performance of salt spray is stable, the overall trend and hydrophobic angle trend is consistent, impact resistance performance has passed the test. Taken together, in the next experiment, the modified SiO2 dosing was determined to be 0.50%.
effects of fluorowax dosing on hydrophobicity and corrosion resistance
low surface energy is one of the prerequisites for hydrophobicity. In order to determine the optimal dosage of fluorowax, the curing temperature is now set at 130 degrees C, the curing time is 20min, the curing agent dosage is 21%, the SA-186 dosage is 0.9% modified SiO2 dosage is 0.5% and other substances dosage unchanged conditions, only change the fluorowax dosage test, as shown in Figure 5. The results showed that with the increase of dosing, the hydrophobic angle showed an upward trend, i.e. the hydrophobic angle increased from 82 to 136 degrees, but when the dosing increased from 0.4% to 0.8%, there was no significant change in the hydrophobic angle. When fluorowax is added to the system, in the melting and curing stage, because fluorine wax in the system is less compatible, so it will surface, on the basis of mastoid form a layer of low surface energy material, thereby reducing surface energy, improve the hydrophobicity of the coating.
is available from Table 5, with the increase of fluorowax dosing, the corrosion resistance of the coating is increasing and then decreasing, and the mechanical properties are stable and then decreasing. Fluorowax dosing increased from 0.10% to 0.40%, corrosion resistance increased from 657h to 766h, but continued to increase, coating corrosion resistance decreased sharply, from 0.10% to 0.40% mechanical properties, can be tested through impact resistance, continue to increase the dosing is significantly reduced. When the amount of fluorowax is reduced, there is no change in viscosity when melting out and viscosity when melting and curing. Fluorowax in the curing melting stage, all float to the surface, on the rough structure to form a waterproof layer, so that water and other difficult to further contact with the coating, directly reduce the possibility of electrochemical and chemical corrosion, and thus improve corrosion resistance. Compared with the rough structure, the anti-corrosion performance is further enhanced, the coating appearance is good without flow hanging and other ills, but when the amount is more, it greatly increases the viscosity when melting extrudes and the viscosity when melting cures, resulting in the formation of sand pattern on the coating surface. As shown in Figure 5F, the mechanical properties of the coating are greatly reduced. Taken together, the fluorowax dosing was determined to be 0.40% in the following experiments.
2.6 Effects of modified graphene dosing on corrosion resistance
Graphene has excellent corrosion and mechanical properties, while pure epoxy coatings are not resilient enough to significantly improve the mechanical properties of the coating when added. However, graphene density is small, easy to reunite, difficult to disperse, so that the mix fluffy, resulting in melting extrusion stage is not easy to feed. It is modified with niacin sulfate, which is available from Figure 6 and adsorbed to the graphene sheet layer, which can not only prevent the reunion of graphene, but also improve dispersion, which can perfectly solve the melting extrusion stage.