Research on Antibacterial and Antifungal Agents for Powder Coatings

1 Introduction: With
quality of life, antibacterial anti-mold products are becoming more and more popular with consumers. From the traditional metal substrate field (home appliances, building materials, transportation equipment, machine housing), expanded to non-metallic substrate field (plastic products, glass products, medium density fiberboard, etc.). In some special occasions or public places, antimicrobial products are essential, such as: hospital ICU ward equipment facilities surface, public transport is prone to cross-infection equipment facilities

. In household equipment, such as refrigerators, freezers, dishwashers, washing machine casings, kitchen cabinets, store food racks and other products that often come into contact with water, are particularly prone to bacteria and mold. In solvent-based coatings gradually withdraw from today, powder coating applications are gradually expanding, powder coatings are often used in a humid climate, moderate temperature environment, coating surface may be contaminated by bacteria, mold and other harmful microorganisms, resulting in film staining, color change, powdering, shedding, loss of the protection of the substrate decoration function, if harmful bacteria and human contact will also infect a variety of diseases, threatening human health. Since 2000, foreign antimicrobial enterprises have flocked to the Chinese market, seizing the high-end market of China's antimicrobial industry, Japanese enterprises represented by silver ions, as well as European and American multinational enterprises with organic materials as the main body. These enterprises have developed antibacterial powder coatings have been widely used in home appliances, automobiles and other fields. In recent years, China's antibacterial coating field has also made great progress, especially in the field of liquid coatings, antibacterial coatings, anti-mold coatings have been widely used in all aspects of people's lives. However, in the field of powder coatings, powder antibacterial agents are rare, mainly by powder coatings before spraying a high temperature mixing process with resin. Most antimicrobials fail during this process, and antibacterial properties are greatly reduced. Tianshi Blue Shield through a long period of antibacterial anti-mold agent screening, identified a compound anti-bacterial anti-mold system applied to powder coatings - Blue Shield LD540, in-depth study of anti-bacterial anti-mold on the use of powder coatings and antibacterial properties. Blue Shield LD540 powder coating antibacterial agent, using nanomaterial encasing technology, effectively protect the high temperature failure of antibacterial agent and high temperature yellowing problem. In low addition, the antibacterial rate reached more than 99%.
2 Test Part
2.1 Preparation of anti-bacterial anti-mold powder
a certain proportion of antibacterial anti-mold powder materials are mixed with pure polyester and pure epoxy resin, fully mixed evenly. Melting and mixing through the twin screw extruder, the flakes are cooled, crushed, and then placed in a grinder to crush into a suitable powder coating with a suitable particle size.
the appropriate amount of antibacterial anti-mold powder coating, sprayed with electrostature spray gun on the sample, placed in the oven at the set temperature, curing the specified time, remove, room temperature placed 24 h. According to GB/T21866-2008 antibacterial coating national standard detection method to detect its antibacterial properties. The impact, bending and scratch resistance of the samples were detected separately.
2.2 antimicrobial volatile performance detection
common antibacterial anti-mold agents are susceptible to light and heat and produce color changes. Antibacterial anti-mold powder coatings are subjected to baking temperatures above 180 degrees C. Therefore, it is important to bake at high temperatures to produce smoke or color changes in the antibacterial agent itself. The antibacterial powder was weighed separately in a constant crucible and placed in a Muffer furnace to test the change of weight, color change and smoke conditions of antibacterial agents at 150 degrees C, 180 degrees C and 200 degrees C respectively.
2.3 Bending, impact, scratch detection
direct reference method standard GB/T 1732-1993 "paint film impact resistance measurement method", the positive flushing model coating film is flat on the impact of the impact device on the iron shovel, back-flushing when the sample coating film is flat on the impactor on the impact.
Direct reference method standard GB/T 1732-1993 Lacquer film impact-resistant measurement method, the positive flushing model coating film is flat on the impact of the impact device on the impact test, back-flushing when the model coating film is flat on the impactor on the impact test.
direct reference method standard GB/T 9286-1998 "color paint and varnish paint film slicing test." On the hard substrate, when the thickness of the coating film is (0 to 60) m, the pitch is 1mm, and when the coating thickness is (61 to 120) m, the pitch is 2mm.
2.4 Antibacterial performance testing
in strict accordance with GB/T21866-2008 required microbiological testing methods, respectively, 0.4-0.5 ml of test bacteria droplets added to the negative control model (A), blank control (B) and antibacterial coating sample (C). Cover the model with sterilized membrane, so that the bacteria evenly contact the surface of the sample plate, in a flat dish, at 37±1 degrees C, relative humidity>90% of the conditions of culture for 24 hours. Then, wash, culture, count, and calculate the antibacterial rate.
3 Results and discussion
3.1 temperature resistance
powder coating in the coating process needs to withstand the temperature test of more than 180 degrees C, which requires the antibacterial agent itself unchanged color, less volatile, no smoke phenomenon. As can be seen from Table 1, LD540 bakes at a temperature of 150-180 degrees C for 20 minutes, the color of the antibacterial agent itself has not changed, no smoke, volatile points (containing moisture) are very few. The LD540 meets the basic requirements of powder coatings.
Table 1 LD540 Temperature Resistance Test:
Note: Volatiles contain moisture
3.2 Bending, Impact, Scratch Detection
Table 2 LD540 Bending, Impact, Scratch Detection (Curing Conditions Polyester Baking 180C/20min, Epoxy 120C/20min)
Figure 1 Scratch-resistant detection
scratch-resistant performance: As can be seen from Tables 2 and 1, the addition of antimicrobials from 0.1% to 2.0% of scratch-resistant properties has passed the test under scratch-resistant conditions from 1000g to 2000g. The addition of antibacterial agents does not affect the scratch resistance of powder coatings.
2 Bending Performance Detection
Bending Performance Detection: At the 2mm full test standard, the bending performance passes when the antimicrobial content reaches less than 2%. It is stated that the addition of antimicrobial agents does not affect the anti-bending properties of the powder coating.
Figure 3 Impact Resistance performance
Impact resistance performance: Figure 3 shows that with the increase of antibacterial capacity, impact resistance performance gradually decreased, when the antibacterial content of less than 1%, antibacterial agents have no effect on impact performance;
From Table 2, Figure 1, 2, 3, it can be seen that, whether it is polyester system or epoxy system, the amount added in antibacterial agents is less than 1%, on bending performance, impact performance, scratch resistance performance has no effect.
3.3 Antibacterial performance testing
According to GB/T21866-2008 standards, antibacterial coatings are divided into two levels, Grade I and Level II, Class I antibacterial rate requirements of more than 99%, suitable for places with high antimicrobial requirements, level II antimicrobial rate requirements of more than 90%, suitable for places with antibacterial performance needs. As can be seen from Table 3, the antibacterial rate of LD540 antibacterial agents reached more than 99% when the amount added was 0.5%. Grade I antibacterial standards have been met. Further increase the amount of antibacterial agents, antibacterial rate increase is not obvious, from the point of view of cost and antibacterial effect, antibacterial agent LD540 in the case of 0.4-0.5% of the added amount is more appropriate, not only to meet antibacterial needs, but also to reduce costs.
3 LD540 antibacterial properties (180 degrees C, 20 minutes) (test standard GB/T21866-2008)
Table 4 LD540 antibacterial properties (120 degrees C, 20 Minutes) (Test standard GB/T21866-2008)
From Table 3, it can be seen that for pure polyester system, antibacterial agent additions in 0.4-0.5%, antibacterial rate of more than 99%, can reach the I-level standard. From Table 4, it can be seen that for pure epoxy system, the amount of antibacterial agent addition is about 0.3-0.4%, the antibacterial rate can reach more than 99%, to meet the standard requirements of Class I antimicrobial agents.
4 Conclusion
(1) Powder coating antibacterial agents need to withstand temperature tests above 180 degrees C, the antibacterial agent itself does not change color, less volatile, no smoke phenomenon.
(2) the addition of antimicrobial agents needs to test its impact resistance to polyester resins, epoxy resin systems, scratch resistance, bending resistance.
(3) antimicrobial agent is not the more added the better the bactericidal effect, in the appropriate addition range, to reach the antibacterial rate of more than 99%, choose the appropriate amount of economical addition range can be.
(4) LD540 antimicrobial agent has little effect on the thermal stability of powder coating color and the mixing between materials in the appropriate amount of addition.
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