In order to meet the needs of users, aluminum for construction is generally surface-treated before it can be put on the market. There are currently three methods for surface protection of architectural aluminum: (1) Anodizing, aluminum alloy doors and windows have been introduced in the 1950s, and are still common surface treatment measures for aluminum doors and windows; (2) Electrophoresis after anodization Acrylic resin, which was commercialized in Japan in the 1960s, was used in Europe in the 1970s and is currently used mainly in Asia. The technology has now been developed from transparent glossy film to matt transparent film and color film, the variety is more diversified, industrial control and product quality are relatively stable; (3) Electrostatic spraying after chemical conversion treatment includes electrostatic powder coating and electrostatic liquid phase Spraying, electrostatic liquid-phase spraying of fluorocarbon resin In the 1960s, the United States has achieved commercialization. The electrostatic powder coating thermosetting polyester coating was commercialized in Europe at the end of the 1960s. It is still a surface treatment method that is dominant in European countries. Today, the single anodized aluminum doors and windows are significantly reduced in Japan and the United States to electrophoretic coating, white electrophoretic coating developed rapidly, and has been applied in Europe. Electrostatic powder coating has become the preferred surface treatment method in Europe and America due to its diverse colors, convenient control, environmental protection, and excellent performance. In recent years, the electrostatic powder coating market is rapidly expanding in China.

1. Technical Prospects for the First 10 Years of the 21st Century

There is no essential difference in the surface treatment technology of aluminum profiles in China compared with foreign countries, but there are still many gaps compared with foreign advanced levels in terms of technological level, equipment conditions, technical management, environmental protection factors, quality indicators and product quality. The authors recently conducted field trips to Italy, Germany and Japan, and communicated face-to-face with foreign counterparts, summarizing the following aspects, as reference and reference for China's architectural aluminum surface treatment industry in the next ten years of technological development.

1.1 Clean anodic oxidation process pays more attention and development

As China's environmental awareness continues to increase, the clean technology will inevitably continue to develop. The anodizing process produces closed-loop recycling of waste liquids from various processes, and gradually achieves low-emissions (zero-discharge) processes that have been adopted in Europe and Japan. Zero-emission cleaning is undoubtedly the direction that the industrial world is pursuing. Due to technical and financial reasons, it can only be carried out in steps in our country.

1.2 Electrostatic powder coating process is more popular

Due to the rich colors and good environmental benefits, electrostatic powder coating has developed more rapidly in China. The coating powder will also develop toward high grades, and the appearance of the coating will also develop from monochromatic to more decorative, such as wood grain, marble and patterns. Electrostatic powder-sprayed aluminum profiles generally have only a single uniform color. The wood grain and marble appearance is similar to the screen printing process on the original powder coating. The second color powder is added to the original powder coating, and then unified. Curing treatment, which means that the new process can only be achieved by adding equipment on the basis of the original spraying equipment. Can be used for aluminum profiles, more suitable for aluminum surface treatment. Another kind of pattern and pattern effect is the transfer method, that is, on the basis of the first spray layer, the plastic pattern or the wood grain pattern on the paper is transferred to the surface under heating. This method is simple and easy. The key lies in The life of the pattern on the transfer printing.

Chemical pretreatment of powder coating, from the environmental considerations, should develop low-chromium and chromium-free chemical conversion treatment. From the standpoint of overcoming the filiform corrosion, it is also possible to use an anodized film as the underlayer of the powder sprayed layer, both of which are the best alternatives to the chromate treatment. The chromium-free chemical conversion coating additives should be China's eager to develop varieties.

1.3 Electrophoretic coating can resist the pollution of the atmosphere

Both the ED film and the powder coating are high-polymer coatings that can effectively resist the pollution of the atmosphere and the marine atmosphere.

The anodic oxide film under the ED film does not present the risk of filamentous corrosion under the film, and it is expected to be an ideal surface treatment method for polluting the atmosphere. For a long time our impression of electrophoretic paint is only transparent polypropylene resin, in recent years, Japan's electrophoretic paint regardless of species or quality have changed significantly. In addition to the transparent glossy paint that we are familiar with, there are matt paints and white electrophoretic paints, which have been used in the construction of aluminum doors and windows. As for the quality of electrophoretic paint can already be comparable with the powder coating.

1.4 Anodizing Technology Advances for Energy Saving

As we all know, the anodizing process parameters have not changed for decades, the solution's sulfuric acid concentration and aluminum ion range, temperature and current density have been included in national standards. In order to improve the anodic oxidation efficiency and accelerate the film formation rate, it is necessary to increase the current density as much as possible while ensuring the performance of the oxide film, and to find ways to improve the film formation factor.

More than 1.5 colors have always been the goal of coloring

The electrolytic coloring of the aluminum anodic oxide film is monotonous in bronze, and the search for multi-color has always been the goal of anodizing workers. Dyeing can obtain a variety of colors, but the poor lightfastness is not suitable for outdoor use, and one color is very troublesome for a trough, and compound coloring still can not get rid of the above difficulties, nor has it achieved large-scale industrialized production in Europe. The use of the principle of light interference to obtain various interference colors of blue, gray, green, yellow, and purple has been reported in a large number of literatures, but it has been regarded as a laboratory process that is difficult to control industrially. In recent years, Italy and Japan have produced more than 10 multicolored production lines around the world, and Japan calls it three electrolytic processes. .

1.6 The development of new technologies

There are many new technologies in the study, some may be close to the commercialization stage, and some only stay in the laboratory stage. Development of new technologies

First, in Japan, a periodic reverse current technique was used to perform electrolytic etching in anodized sulfuric acid solution to remove extrusion striations. Although the technology is still in the experimental stage, once successful, it has very important technical and economic value, and can fundamentally change the pretreatment method of aluminum.

The second is the computer design developed by New Zealand. Through two anodizing processes, two colors of decorative patterns can be obtained. The aluminum plates used as interior decoration are unique and creative, demonstrating the connotation of the artistic effects of aluminum.

In addition, with the rapid spread of spraying, ecological pretreatment technology and chromium-free additives are bound to develop. Compared with foreign countries, our country is lagging behind. In the next 10 years, our country will certainly receive attention and rapid development.