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Zhang Baozhong 1, Yan Surong 1, Zhang Lide 2, Fang Keming 3
1. Zhongke Jetta Nano Application Technology Co., Ltd.;
2. Institute of Solid Physics, Chinese Academy of Sciences;
3. Beijing University of Science and Technology
01 Introduction
With SiO2, ZnO, TiO2 3 kinds of nanomaterial composite modified powder coating, significantly improve the adhesion and corrosion resistance of the coating film, the nanomaterial composite powder coating on aluminum alloy profiles without chromium passivation coating.
product performance fully meets the requirements of the relevant national standards and line standards, some performance exceeds the corresponding traditional coating product performance.
powder coating is a low-polluting coating, solids close to 100%, the use of electrostectrectectration spraying, pipeline operation, theoretical product utilization rate of nearly 100%
.
construction can form a thicker coating, film-forming process can be controlled in less than ten minutes to complete, so the film-forming efficiency is high.
the mechanical properties of powder coatings and the resistance to chemical corrosion. Because of these outstanding advantages, the development is very fast. Domestic powder coating growth in recent years can be seen in Table 1.
powder coating is mostly used for metal coating, before coating should be passivated treatment to increase the adhesion and corrosion resistance of the coating film. But passivants are Cr6 plus, which contains a carcinogenic risk and pollute the environment.
only to aluminum alloy profile coating considerations, according to statistics, in 2007 China produced aluminum alloy profile 6.94 million t, of which at least 3 million t aluminum profiles with powder coating.
Per t aluminum profile "passivation" treatment needs to consume 2.3 kg chromium (chromate), the country's annual aluminum profile "passivation" treatment needs to use 7,000 t chromium agent, each t aluminum profile coating needs to discharge 4.5 t chromium waste liquid, annual emissions of more than 13.5 million t, waste liquid treatment costs are high.
of toxic waste liquid containing Cr6 plus is causing serious pollution, and online coating workers are the first victims. According to incomplete statistics, there are more than 680 aluminum profile enterprises in China, plus other enterprises using powder coating a total of about 7,000, small scattered powder coating enterprises difficult to count, chromium waste liquid emissions are very harmful.
during the 12th Five-Year Plan period, china should further strengthen the prevention and control of heavy metal pollution. Therefore, the removal of "chromium passivation" process is not only related to the sustainable development of powder coating, but also related to the national economy and people's livelihood, a major event, of great significance.
This paper uses nanomaterials to transform the general purpose powder coating used inside and outside the home, trial production of successful nano-composite powder coating, no chromium passivation coating aluminum profile coating of the performance indicators all meet the requirements of traditional chromium passivation coating, some performance is still more than.
by the aluminum profile production enterprise statistics, aluminum profile chrome passivation treatment cost of about 120 yuan / t, after removing the "chrome passivation" process, will save hundreds of millions of yuan per year, there are obvious economic benefits.
the "chromium passivation" process of nano-composite powder coatings, the increase in costs is not much, cost-effective. In addition to the aluminum profile industry, it is also suitable for coating applications in the coating industry such as coils, vehicle and machine manufacturing, home appliances, metal structures, aerospace, shipbuilding, petroleum pipelines, medical devices and the mechanical and electrical industries.
02
1.1
epoxy resin (internal) and polyester resin (external) for powder coatings. Composite nanomaterial ZKNM-01: consists of siO2 (enhanced surface effect and tactile effect), ZnO (enhanced electrostectrectile effect), TiO2 (enhanced optical properties) 3 nanomaterials.
pigments: titanium white powder, silicon aluminum powder, BaSO4.
additives: leveling agents, brighteners, scents (preservatives), balance agents, curing agents, etc.
1.2 Manufacturing process
1) composite nanomaterial ZKNM-01. After many tests, the relative proportion of the three nanomaterials mentioned above was determined, the mixture was uniform, the surface modification was carried out by physical and chemical methods, and the specification was 20 to 60 nm.
2) nano-composite powder coating preparation. Nano-composite powder coating using secondary melting technology process, the process flow can be seen in Figure 1.
1.3 Product testing and
nanocomposed powder coating formulations can be found in Table 2.
: (1) Polyester resin can also be selected DSM 5200, 5201;
composite powder coating developed by the company, coated with a chrome-free passivation process, laboratory curing conditions and ordinary powder coating curing conditions are the same, 180 degrees C/15 to 30 min curing.
composite nano-powder coating and the resulting coating of the physical mechanical properties, corrosion-proof performance according to HG/T 2006-2006 "thermo-solid powder coating" and GB / 5237.4-2008 "aluminum alloy building powder spray profile" detection.
the shape of the composite nano-powder coating, the structure and appearance of the cured coating film are indicated by a scanning electron mirror (SEM) and a transmission mirror (TEM).
03 Results and Discussion
2.1 Results
1) Uniform dispersion of nanomaterials in powder coatings
2) Test results
nomethium composite powder coating (chromium-free passivation treatment) by the National Chemical Building Materials Testing and Certification Center testing, all technical indicators in line with HG/T 2006-2006 quality standards, test results see Table 3.
3) Practical application test
On December 1, 2009, the actual use test was carried out at the Guangdong Firma aluminum profile plant, and the test was recorded in Tables 4 to 5.
Under the same coating conditions, the electrostitive effect of the nano-composite powder coating was better than that of the other 3 commonly used powder coatings, the powder rate increased by 16.36% on average, the coating loss was less, the coating utilization rate was high, the film thickness, and the coating efficiency was high.
samples were tested by the Beijing Metallurgical Product Quality Supervision and Inspection Station, and the product quality met the GB 5237.4-2008 standard requirements, and the quality of the control samples was the same.
2.2 nanometer material enhances film tightness
after nano-modified composite powder coating to improve electrostitectrulation performance, in the electrostitive spraying process, under the combined action of air pressure power and static electricity, particle size particles with large charge, fast flight in the air.
and under the effect of the same electric rebuke, first fly down and evenly line up on the aluminum alloy substrate surface, small particle size particles due to low charge, and then fly down.
And under the coulomun force, can only be filled in the micro-pores of particles with large particle sizes in turn, repeated in turn, so that the different sizes of component particles in the coating can be evenly distributed in the coating, compared with traditional powder coatings, the formation of a denser powder coating.
nano-composite powder coating melts and levels at high temperature, while film resin and curing agent cross-link reaction, so that the coating membrane structure to the network development,
filled into the large particle micro pores nanoparticles, the surface of the active group and resin or curing agent molecules in the active group cross-linking reaction, micro pores play a "closed hole" effect, so that the film's compaction is enhanced.
the shielding effect of the whole coating film, improve the permeability of water and oxygen, and enhance the corrosion-proofing effect of the coating film. This is the chrome-free passivation of nanomaterial composite powder coating film can improve the anti-corrosion effect of an important reason.
2.3 nanomaterials to improve the coating adhesion of powder coatings
traditional powder coatings and nanomaterial composite powder coatings are coated under the same conditions on aluminum alloy substrates, respectively, and the resulting coating film is analyzed with a transmission mirror to analyze its interface status.
The former coating and aluminum alloy interface there is a transitional chrome passivation layer, it is on the one hand and aluminum alloy bottom closely bonded, on the other hand with the coating on top of it is also closely bonded, improve the coating adhesion, because of the close binding with the coating, shielding effect is enhanced, so the chrome passivation layer can improve adhesion and corrosion resistance. There is no transitional passivation layer between the coating film and the aluminum alloy surface from the coating of
nanocomposite powder coating (dechromium passivation), due to the strong reaction properties of particles such as nano-size TiO2, and the reaction group produced by the new clean surface of the aluminum alloy after pre-treatment (except chromium passivation).
The strong interaction and bonding of the two, so that some TiO2 nanoparticles embedded in the aluminum alloy surface gap or active point and firmly bonded, and these nanoparticles and the coating resin or curing agent of the active group reaction, increase the coating and aluminum alloy surface bonding strength, thereby improving the adhesion and corrosion resistance of the coating.
The interface between the coating and the aluminum alloy surface is further studied with a transmission mirror (magnified by
1 million times), which induces the formation of an alumina microfilm layer on the aluminum substrate surface during coating spraying and curing; The structural analysis of coating form, structure, coating film and aluminum alloy surface formation formed by
nanomaterial composite coating on aluminum alloy surface provides a theoretical basis for the process of chromium passivation processing in the removal coating and the performance of coating film obtained by the traditional coating process of powder coating.
04 Conclusion
1) using SiO2, ZnO (enhanced electrostectrical effect), TiO23 nanomaterials, according to a certain proportion of mixed nanomaterials, with physical and chemical methods to modify nanoparticles, to obtain a stable dispersion of composite nanomaterials.
With this nanomaterial and general purpose powder coating, by the secondary melting process, the nano-composite powder coating, confirmed by a series of small and expanded tests, the process is easy to run, the product dispersion is good, storage is stable.
2) Nanomaterial composite powder coatings have the following improvements in performance:
(1) improves the electrostitive effect of the coating, improves the powdering rate of electrostectrectile spraying
(an average increase of 16.5%);
(3) Analysis of the coating status, coating and interface structure of the nanomaterial composite powder coating with a transmission mirror found that, due to the strange effect of nanomaterials, the bonding strength of the coating and aluminum alloy surface was greatly increased, which significantly improved the adhesion of the coating.
the role of nanomaterials, so that the powder coating on aluminum alloy profile coating can successfully leather chromium passivation process, product performance fully meet national and industry standards.
。