Research on the preparation and application of ETFE powder coatings

Abstract: With the increasing demand of environmental protection for the semiconductor and electronics industry, China's semiconductor industry is booming, and the demand for corrosion-resistant, combustion-resistant wind pipes has increased dramatically. The market for fluorine-containing powder coatings is growing significantly. The research on the preparation, performance and application of powder coatings of San Aifu company is mainly described

. The results show that THEFE powder coatings of Shanghai San Aifu Company can be used in corrosion-resistant lining areas such as wind pipes, chemical storage tanks and headers.0 Foreword
Although Teflon (PTFE) has good chemical resistance, almost any strong acid, strong alkali, strong oxidant and solvent does not work on it at high temperatures. However, the processing and molding of PTFE is more difficult, coupled with the metal equipment can not be well combined, so that PTFE's mechanical strength is low, line expansion coefficient and other physical properties are not enough to emerge, and excellent chemical performance can not play its role. Ethylene-Teflon copolymer (ETFE) is a partially fluorinated, meltable fluorine resin, which is used as a coating, in addition to high and low temperature resistance, anti-viscosity, wear resistance, electrical insulation and moisture absorption, compared to other fluoroplastics, ETFE has a better toughness and stretch strength, so it is ideal for explosion-proof applications. Because the surface is sprayed into a film to produce a non-stick effect, so the surface can hardly produce static electricity, widely used in flammable and explosive occasions. In particular, the state invested a lot of money in semiconductors, electronics and other industries, coupled with environmental protection needs, the demand for clean room corrosion-resistant wind pipes surge, fluorine powder coating market is also significantly increased.
fluorine powder coatings used in wind pipe linings are available in two types: ethylene/TEF co-polyplymer (ECTFE, trade name Halar) powder coatings and ETFE powder coatings. This study used ETTE base resin produced by Shanghai San ai Fu New Materials Co., Ltd. to make powder coating. The performance of the base resin, the preparation and performance characteristics of the powder coating are mainly studied, and the case of the spraying parts is listed, and the performance of the film after spraying is studied.
1 Test Part
1.1 Test Raw Materials
The basic resin for the preparation of ETTE powder coating is an ETTE resin produced by Shanghai San Aifu New Materials Co., Ltd., with a melting point of 240 to 260 degrees C and a melting index of 6 to 20g/10min.
1.2 Test Method
1.2.1 Smash
the ETFE base resin was crushed using the LHL-type airflow shredder of Weifang Zhengyuan Powder Engineering Equipment Co., Ltd. The compressed air pressure is 0.8MPa. After the compressed air is frozen, filtered and dried, supersonic air flow through the nozzle is injected into the rotating crush chamber, making the material flow. In the rotating crushing chamber, the accelerated material meets at the jet stream junctions of several nozzles, resulting in violent collisions, frictions, shears and ultra-fine crushing of particles. The crushed material is transported by rising air flow to the impynor grading area, and the separation of the thick powder is achieved under the effect of the centrifugal force of the graded wheel and the pumping force of the fan. Thick powder due to its own gravity back to the crushing chamber continue to crush, qualified fine powder with air flow into the cyclone collector, fine dust collected by the bag dust remover, purified gas from the fan discharge. The particle size of the crushed ETF powder is adjusted by adjusting the graded series.
1.2.2 electrostature spray
requires warm-up of the work parts and is sprayed with Gema's OptiFlex2 F model hand-held electrostature spray gun. Typically, a cold electrostitive spray is performed on a primered work piece, which is built on top of the MELT point of the ETTE for a period of time to obtain a smooth coating. Then quickly take the workware out of the oven and spray a layer of ETF powder again over the ETF melting point at the temperature. Since the part of the powder that comes into contact with the heat melts, more powder adheres to the work piece until the melting stops. This process can be observed with the naked eye because the melted ETF is very bright. When the sprayed ETF is no longer melted, put the work piece in the oven again, keep warm above the melting point for a period of time, and repeat the above process. Each spray can increase the coating thickness by 0.1 to 0.2mm.
1.2.3 neutral salt spray test
neutral salt spray test according to the standard GB /T1771-1991 method.
1.2.4 acid-base-resistant test
test film preparation method is as follows: THE ETTE powder coating sprayed on 10mm×50mm×1mm carbon steel plate, oven temperature of 290 oC, test film spray 0.5mm thickness OFTE coating.
test sheet coated with ETF is soaked in a solvent at a temperature of 25 degrees C, of which 3/4 of the test plate length is long-term impregnated in the solvent.
test solvents are NaOH solution (250g/L), 50% HNO3 solution, 50% acetone solution, 30% hydrochloric acid solution, 30% sulfate solution, 30% ethanol solution and styrene.
1.3 Analysis and Symptoms
1.3.1 DSC Test
Take 6 to 10 mg ETFE samples into the sample pool and increase the temperature from 150 degrees C to 300 degrees C at a warming rate of 10 degrees C/min to record changes in the curve. The DSC test instrument is the DSC8000 of Perkin Elmer, USA.
1.3.2 MI (Melting Index) test
ETFs are tested in accordance with the international standard ASTM-3159. The test was performed at a load of 5kg and a temperature of 297 degrees C, using the MI-3 melt index instrument from Goettfert, Germany.
test for 1.3.3 element content
the fluorine content of THEETFE resin was tested using TheOxford-instrumentsMQC-23-55 NUCLEAR magnetic resonance instrument at 40 degrees C. This method has been peuged with titration.
1.3.4 particle size distribution analysis
using Malvern's MASTERSIZER 2000 laser particle size meter to analyze the particle size distribution of ETFE powders. The sample method is to dilute the dispersed ETFE powder with waterless ethanol, put it into the ultrasonic instrument for ultrasonic dispersion, and then put it into the instrument to test the particle size distribution, and obtain D10, D50 and D90 data.
1.3.5 thermal weight analysis
the thermal stability of THEFE powder is analyzed using the Lych TG209F1 thermal heavy analyzer. Take 6 to 10 mg ETFE samples into the sample pool, in the nitrogen atmosphere, at a temperature of 10 degrees C/min from room temperature to 450 degrees C, according to the analysis requirements, even need to heat up to 800 degrees C, record the quality changes of the ETFE powder sample.
1.3.6 Analysis of mechanical performance and relative density
According to the standard sample, the ETTE test film is tested with a capability performance tester at 23 degrees C, and the tensile strength and fracture elongation rate are tested according to GB/T 1040.1-2006. Press GB/T 1033. The provisions of Law A in 1-2008 are tested for relative density.
1.3.7 Other analyses
linear expansion coefficients, dielectric constants, volume resistivity, and arc-resistant oxygen index are intersected with third-party inspection facilities certified by CMA and CNAS.
2 Results and discussion
2.1 ETFE basic resin performance
ETFE powder coating is generally used in the field of heavy corrosion and explosion prevention, the basic resin has certain requirements, the mechanical properties of resins, electrical properties, thermal stability and melting fluidity are required. The performance test results of the ETFE base resin are shown in Table 1.
2.2 Powder Coating Performance
2.2.1 Particle Size Distribution Results
The average particle size of ETFE powder coatings used for powder coating is 35 to 90 m. Smaller powder sizes are beneficial, but fluidization is more difficult and consistency is poor. In practice, it is found that too much powder content of less than 20 m will cause the electrostation gun to clog, which will make the spraying process difficult to control. And because ETFEs are mostly used in chemical heavy anti-corrosion, the application of thin coating is relatively small. A larger average particle size, especially a powder with a particle size greater than 100 m, will be reduced compared to the surface area, resulting in a powder with an electrostial charge not enough to spray on the work piece, greatly reducing the powder rate, resulting in electrostectrulation spraying can not be carried out.
powder coatings with different particle size distributions are prepared according to the needs of thin and thick coatings. However, due to the particle size requirements of the spray gun, the D90 needs to be less than 190 m. Figures 1, 2 and 3 are particle size maps of different graded powder coatings during airflow crushing.
test of the powder coating with different particle size distribution is carried out, and the test results show that the small particle size is beneficial to improve the powder rate. However, the particle size is too small, the thickness of each spray will be smaller, spray the same thickness of the film, small particle size powder coating needs to increase the number of sprays. Therefore, an ETFE powder coating with an average particle size of 50 to 60 m is recommended.
2.2.2 thermal re-analysis results
during the spraying process, the powder coating heating temperature can reach up to 320 degrees C. At this temperature, ETFE breaks down, producing toxic substances. Therefore, the ETF powder coating with 3 different batch numbers has a constant temperature of 4h at 300 degrees C and a constant temperature of 1h at 450 degrees C, resulting in a weight loss curve shown in Figure 4.
can be seen from Figure 4, at a constant temperature of 4h at 300 degrees C, San Aifu (3F) ETF powder coating weight loss is lower than foreign imports.
2.2.3 Melting Index results
ETFE stays above the melting temperature for a longer period of time during the spraying process. In general, polymers are subjected to heat for too long above the melting temperature, resulting in small molecules, resulting in an increase in the melting index, resulting in a flow-hanging phenomenon.
at 297 degrees C, the melting index of powder coatings is listed in Table 2 with changes in heating time. As can be known from Table 2, the heating time of the coating at 297 degrees C is as high as 120min, and the trend of increasing the melting finger does not exceed 1.0. This powder coating does not have significant thermal decomposition as the heat time increases, which is consistent with the test results of the TGA.
2.2.4 Results of the neutral salt
test are listed in Table 3. The results showed that when the test time was 15d and 30d, the test film did not lose light, did not foam, and was not damaged. At the test time of 60d, the test film had a slight loss of light, but there was still no foaming or damage.
2.2.5 Test results for acid-base and solvent resistance
The test results for long-term immersion in acid-base and solvent are listed in Table 4. When the immersion time exceeds 180d, the test film appears to varying degrees of loss of light, no foaming, no damage, no corrosion cracking, shedding or other adverse phenomena.
2.3 Examples of powder spraying
Figure 5, Figure 6 and Figure 7 are examples of parts sprayed using the above powder coating, respectively, wind pipe and chemical storage tank, the former coating thickness of about 0.3mm, the latter coating thickness of about 1.2mm. Passed the film thickness, electric sparks and adhesion tests.
3 Conclusion
USETFE base resin produced by Shanghai San ai Fuxin Materials Co., Ltd. is used to obtain a powder coating with suitable particle size distribution through airflow crushing, and to conduct a powder coating test. The results show that the particle size distribution, heat resistance, fluidity and powdering rate of powder coating can meet the needs of electrostature spraying process. The results of neutral salt spray test, acid-base resistance and solvent test show that the prepared powder coating has significant anti-corrosion effect on the chemical substances used in this study. Spraying practice on work parts of different sizes, film thickness can be adjusted from thin to thick to meet the needs of the wind pipe industry, chemical storage tanks and other equipment needs anti-corrosion lining. More corrosive tests such as acid and alkali and solvents are still under study.