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 favored 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 the United States 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. Technology development in the 1990s In the past 10 years, aluminum materials (especially aluminum profiles) in China have grown by leaps and bounds, and the production scale of aluminum profiles has approached 1 million tons per year. Driven by advanced foreign technology and imported equipment, China's aluminum production technology has made new advances in anodizing process and equipment, and established new production lines such as electrostatic powder coating and electrostatic liquid coating and electrophoretic coating. The cutting-edge technology has sprouted in our country, with different degrees of development.
1.1 Anodizing Pretreatment Process The purpose of renewing the anodizing pretreatment is to remove the natural oxide film, grease and impurities on the surface and obtain a uniform and clean aluminum surface, which is conducive to the formation of a high-quality anodized film. Users in our country also require the removal of extrusion striations to achieve a uniform aesthetic appearance. Alkaline etching was used to obtain a matte surface in early stages, but excessive etching caused large aluminum loss, typically 3% to 5.5%. This not only increased costs, but also caused serious environmental problems. The formation of a matte surface was accompanied by the inherent nature of exposed profiles. The organizational flaws. Since then, Japan has introduced an acid etching method in our country (which is basically not used in aluminum profiles in Japan). Due to the low aluminum consumption (which can reach about 1%), the surface details were once welcomed by Chinese manufacturers. However, due to fluoride ions as the main bath, brought about more serious pollution, once caused heated discussions. The mechanical etching method has the advantages of low operating cost, good environmental benefits, and fine and no-scratch surface. It was first applied in European countries such as France and Italy. In the mid-1990s, Fujian Sanyuan Aluminum and Zhejiang Dongliang Aluminum introduced institutional shot blasting machines and mechanical polishing (striping) machines and related processes from Italy and Spain, respectively, which have been operating smoothly and received excellent results. Since then, many factories in Guangdong and Jiangsu provinces have successively imported more than one device from abroad. At the same time, China's self-made equipment has also entered the market. The price is only about 1/5 to 1/8 of the imported equipment. Whether mechanical shot blasting (or sandblasting) or mechanical polishing (mirror or satin finish), aluminum consumption can be controlled below 1%, and the appearance is even and detailed, and the decorative effect is good. According to the domestic and foreign production practices, the author recommends mechanical etching treatment instead of the traditional chemical etching (acid or alkali etching) in order to improve the appearance of aluminum profiles in China.
1.2 Anodizing Process and Equipment Progress The anodizing process has not changed fundamentally in the past 20 years. Hard anodizing technology has made many advances during this period. Breakthrough Anodizing The "spark" anodic oxidation and micro-arc oxidation of the Faraday zone have been commercialized. The recent development of high-speed and high-efficiency anodizing technology (HEA technology) of aluminum profiles has not yet obtained wide industrial applications.
1.2.1 The pulsed anodizing power source was widely publicized and introduced in the 70s and 80s. Since the experimental data is mostly selected from hard films with high current density (eg >3 A/dm2) and subsequently applied in the anodizing process for building aluminum profiles, no significant effect has been obtained and thus no large-scale application has been achieved. Further practice shows that in the production of thick film (film thickness> 20μm), the pulse method is more favorable for the quality of the sealing hole, which shows that the current recovery effect can help the heat dissipation during the formation of the oxide film, reducing the film due to temperature rise Dissolution, to prevent the expansion of the oxide film orifice, is conducive to improving the hardness and density, but also help seal the hole. For aluminum standard anodizing process, the current density is low (usually 1 ~ 1.5A/dm2), the film thickness requirement is only 10μm, the exothermic heat of the oxidation process is not serious, so it does not show obvious advantages. The authors believe that pulsed power is very practical in hard anodized or thick film production.
1.2.2 Ion exchange equipment for removal of aluminum ions Anion exchange equipment for the removal of aluminum ions in sulfate baths is of practical significance for the optimization of process measures. In the past, when the Al3+ in the sulfuric acid bath exceeded 20 g/L, the partial discharge liquid was readjusted, inevitably causing periodical fluctuations in the Al3+ content. In order to stabilize the content of Al3+ in the anodic oxidation bath, some imported lines in China in the 1980s imported Japanese or Italian Al3+ removal devices, which may not be widely used because of the limitations of the technological level and technical management at that time. In recent years, China's own production of "recovery of sulfuric acid automatically to Al3 + device", a device can remove about 100 kg of aluminum per day, thereby controlling the Al3 + in sulfuric acid in the set value, so that the oxidation process is more stable and accurate, and at the same time have a very good environment benefit.
1.3 Coloring Techniques The coloring of various aluminum profiles is traditionally performed using electrolytic coloring (the Asada method, which was invented by Japanese Asada, also known as secondary electrolysis). The interior decoration is also colored with a variety of colors (dyeing method is not suitable for outdoor use). In recent years, foreign countries have introduced polychromization techniques (ie, the use of light interference effect coloring, Japan called the three electrolytic), composite coloring (dyeing and then electrolytic coloring) technology, breaking the electrolytic coloring only bronze frame. However, industrial production has not yet been realized in our country.
1.3.1 Single nickel salt electrolytic coloring system Single nickel salt electrolytic coloring system has gradually increased. In Europe, tin salts have been used for tinting. Because tin salts and tin-nickel mixed salts have strong anti-impurity interference and have little environmental damage, industrial control is easy. China has always been based on tin salts (and tin-nickel mixed salts). Japan, on the other hand, has always favored single nickel salts and is equipped with special power supply and bath purification (such as sodium and potassium) devices. Due to the small color difference of light nickel (imitation stainless steel and champagne) and the reproducibility of tones, nickel salts in China and Europe have developed single nickel salt coloring technology in recent years. The bath composition is in addition to MgSO4, H3BO3, and NiSO4. The content is generally high, about 100g / L, impurities sodium, potassium have to be controlled, depending on the process requirements and different, the Japanese process also controls the content of ammonium.
1.3.2 The introduction of new coloring power supply.
The power supply is not an isolated device, it must be a supporting device for a particular process. There are two kinds of electroless coloring techniques for single-nickel salt imported from Japan in Japan, namely the light UniNier method (uniform coloring meaning) and the new residence method. The power supply is not the same, but it can be considered as a different DC coloring. . The coloring power supply for single nickel salt in Europe is not a simple sine wave AC power supply, such as Spain adopts DC (Direct Current)/AC (AC) power supply, and the United States has DC/AC/Asymmetrical AC power supply. The ELCA company in Italy introduced a multi-functional coloring power supply that can output DC, variable-frequency AC and DC and DC/AC superposition. This power source can be applied to various types of electrolytic coloring and polychromization techniques.
1.3.3 Requirements for diversification of colors The diversification of colors promotes the appearance of new electrolytic coloring baths. Titanium golden selenium salt solution, golden manganese salt solution has been quite common in China, but due to the long-term practice of nickel and tin salts, which are not domestically or internationally tested, these solution-colored aluminum materials are used to seal the hole quality, especially in use. The problem of discoloration and fading in color is still worthy of attention. In the process of anodic oxidation of aluminum materials in China, some practices that are inconsistent with foreign standard processes appear from time to time. They have not been scrutinized and examined (only to reduce costs). The author thinks that there is no effect on long-term use effects and production environment benefits. Less hidden dangers.
1.4 Method of sealing holes Hundred flowers blossoming Currently, the cold sealing hole is still the sealing method for most of the anodized films of aluminum in China's architecture. This is related to the large number of imported processes and equipment from Europe in the 1980s. Cold sealing hole water quality requirements are not high, process control is easy, more suitable for China's production status. At present, Europe mainly adopts cold sealing and high-temperature steam sealing, and the latter seems to have a tendency of development. Japan has not accepted the cold-sealing process so far, favoring hydration sealing in boiling water or electrophoretic (ED) sealing. Compared with the sealing pores of boiling water and the cold sealing pores of Ni and F, the high-temperature steam sealing pores just make up for their shortcomings. The operating conditions are 100 ~ 110 °C, the pressure is slightly higher than the atmospheric pressure, the sealing rate is higher than the boiling water sealing hole Fast, poor control of water quality and pH, no white powder, no loss of organic dyes during sealing, and no environmental pollution (Ni and F). This is a good way to guarantee the quality of the sealing and the environment.
China still has not solved the problem of frequent fluoride ion supplementation during the operation of the cold sealing bath, which has brought great harm to the stability of the sealing process. Domestic factories generally add ammonium fluoride, ammonium hydrogen fluoride, sodium fluoride, or even hydrofluoric acid to supplement fluoride. However, practice has shown that the depletion of fluorine is often exacerbated. Although attempts have been made to ease the use of fluoroborate and fluorosilicates, it has not yet been completely resolved in industrial production.
Since the 1990s, research work and industrial practice in China have proved that pure water washing at 60 to 70°C after cold sealing is a good way to improve the sealing quality, speed up the sealing rate and shorten the testing period, and can even increase the ductility of the oxide film. To prevent the appearance of micro-cracking, hot-water washing is not as good as promoting the drying of the profile, it is better to say "after cold-sealed hole". Drying alone does not replace the "post-treatment" effect of hot water. "Post-sealing after cold sealing" is a technological advancement and it is also a measure worthy of promotion.
1.5 Vertical Anodizing Production Line Anodized aluminum profile production line in China is basically horizontal. The two production lines imported from Japan in the 1980s were not ideal and almost negative. In 1997, Xicai Aluminum Company imported from Japan an annual output of 12,000t automatic anodized electrophoretic paint production line, the technical level and higher yield and quality. At the end of the 20th century and the beginning of the 21st century, Sichuan Fangzhou and Guangdong Jianmei successively put into production the annual production capacity of 20000t and 30000t. In general, the vertical line is suitable for mass production. The annual output is preferably 12,000 to 36,000 tons. At this time, the consumption of chemicals and electric energy is lower than that of horizontal lines, and at the same time, it occupies less land and is easy to automate production. The main drawback is that the construction cost of an investment is high. Taking the monthly production of 1000t as an example, the vertical line is 1.8 times the construction cost of the horizontal line. However, vertical anodizing production lines, especially in the case of electrophoretic painting, should be a better choice in the future.
1.6 Market Share of Polymer Coatings for Aluminum Profiles Expands If an aluminum anodizing process for building aluminum was established in the 1980s, electrophoretic coatings of various types, electrostatic powders, and liquid coatings quickly emerged in the 1990s. Bright acrylic polymer film, colorful powder sprayed polyester layer and fluorocarbon coating with better performance have been established in our country to achieve mass production of production lines, accounting for about 20% of aluminum profile surface treatment products. And there is a growing trend.
The electrophoretic (ED) coating was developed in Japan more than 30 years ago and combines the advantages of anodized film and polymer coating. The ED film is popular in Japan and East Asia for its smooth brightness. Although white and various colors of ED films have been introduced, the construction market is still mainly based on transparent films. Although ED fluorocarbon coatings have been developed in foreign countries, they have not yet been industrialized. All the ED paints were imported from Japan at an early stage. Currently, Taiwan's or domestically-made ED paints are basically used in China. Although their performance is inferior to that of Japanese paints, they can pass national standards.
Powder electrostatic spraying polyester coating is very popular in Europe. Its market share is equal to that of anodizing. Its color is rich, its reproducibility is good, process control is convenient, and its environmental benefits are good. It also has a tendency of expanding in China. Polyester powder China has been able to produce polyester-TGIC, which can meet the needs of the construction industry. The new high-performance powders with better performance recently developed in Europe can be compared with fluorocarbon resins, which have not yet been used in China.
The fluorocarbon resin coating with excellent performance has been applied in China. However, paints can only be imported from foreign production plants. Fluorine-containing polymers are compounds that are known to be relatively stable in the environment. The so-called fluorocarbon coating currently refers to polyvinylidene fluoride (PVDF)-based coatings. The United States PPG company first, and with Kynar as a trademark, fluorocarbon coating plants around the world generally use Kynar500 or Hylar5000 as a base compound compound. At present, China's fluorocarbon coatings are mainly imported from the United States's PPG company, the British ICI company and the United States' Valspar company. The price is high but the performance is very good. According to foreign countries, its outdoor service life is guaranteed for more than 25 years, which is higher than the electrophoretic layer and the electrostatic spraying layer.
Fluorocarbon liquid spray is generally a multi-layer spray, with 2 layers (primer and topcoat) or 3 layers (primer, topcoat, and varnish) being more common, and individual 4 layer processes. Per litre of fluorocarbon paint can generally be sprayed 5m2, according to reports electrostatic high pressure electrostatic atomizer gun can increase the paint rate to 7m2. Due to the extremely high price of fluorocarbon coatings and the large price difference between large batches and small batches, the painting rate should still be an important economic indicator.
2. Technology Outlook 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 in terms of process level, equipment conditions, technology management, environmental protection factors, quality indicators and product quality, etc. There are still many gaps in foreign advanced level comparisons. The authors recently conducted field trips to Italy, Germany and Japan, and communicated face-to-face with foreign counterparts, summarizing the following aspects, as a reference and reference for China's architectural aluminum surface treatment industry in the next ten years of technological development.
2.1 Clean Anodizing Process Pays More Attention and Development As China's environmental awareness continues to increase, the clean process will inevitably continue to develop. The anodizing process is used to produce closed-loop recycling of waste liquids from various processes, gradually achieving low-discharge to zero-discharge processes that have been adopted in Europe and Japan. The anodizing bath uses ion exchange method to remove aluminum ions to recover sulfuric acid; alkaline etching bath uses crystallizer and vacuum filtration to drain aluminum hydroxide to recover alkali; nickel salt electrolytic bath and its washing tank use ion exchange method and reverse osmosis method respectively. Nickel sulphate is recovered and impurities are removed; cold plugging bath solution is used to remove solid precipitates and metal impurities by filtration and ion exchange; ED paint tanks are selected for ion exchange refining and reverse osmosis recovery. All washing water is removed by neutralization, flocculation, clarification and pressure filtration to remove slag, and the clarified solution is recycled and reused after reverse osmosis. The zero-emission cleaning process is undoubtedly the direction sought by the industrial world. Due to technical and financial reasons, it can only be carried out in steps in our country.
In the actual operation and design of the anodizing line, the situation is much more complicated. Alkaline etch baths such as the use of crystallization filtration method, the concentration of sodium hydroxide is bound to be high, at this time can not be very satisfactory matte surface, then the alkaline etch closed loop design should be reconsidered to improve, so in fact it Suitable for mechanical etching process. Similarly, the closed circuit design of other processes must be considered in conjunction with the production process and product characteristics. However, closed circuit design not only has the characteristics of environmental protection, but also makes the process parameters of the anodizing process more accurate, thereby further stabilizing and improving the quality of the anodized film.
2.2 Electrostatic powder coating process is more popular. Due to rich colors and good environmental benefits, electrostatic powder coating is developing more rapidly in China. The coating powder will also develop toward the high-end direction and get rid of the state of a single polyester-TGIC powder. The appearance of the coating will also develop from a single color to a more decorative direction such as wood grain, marble, and patterns. Italy and Germany have exhibited such products in our country. 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. Metallographic identification indicates organic bonding between the powder coating and the substrate and between the two powders. After visiting the Italian NATURALL process workshop, the authors felt that the technical ideas were clear and the process was simple and suitable for use in our country. 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 print.
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 anodic oxide film as the underlayer of the powder sprayed layer, both of which are preferred alternatives for the chromizing treatment. Additives treated with chromium-free chemical conversion coatings should be urgently developed in China.
2.3 Electrophoretic coating can resist pollution The atmospheric ED film and powder coating are both high polymer coatings, which can effectively resist the pollution of the atmosphere and marine atmosphere.
The anodic oxidation film under the ED film does not present the risk of filamentous corrosion under the film, which is expected to be an ideal surface treatment method in the polluted 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. Spain SIDASA company had tested the lightfastness of Honnystone, and compared with the powder electrostatic spraying polyester-TGIC coating, the results show that the color change is basically the same, the coating is not blistering, but the gloss retention rate Honnystone is obviously better than the powder coating Floor. In the 443h exposure experiment, the Honnystone gloss retention rate was still 79% to 81%, while the powder coating remained only 49 to 43%, indicating that the performance of the electrophoretic coating has been significantly improved.
In Japan, 90% of the anodized anodic oxide films for architectural aluminum are sealed by electrophoretic paint, and the other 10% are also selected for high-temperature boiling water sealing. According to the Japanese side, this is related to Japan being an island country, with high atmospheric salt content in coastal areas and related to industrial development through atmospheric pollution. The electrophoretic coating layer has better resistance to the marine atmosphere and pollution of the atmosphere than the sealed anodized film. The authors estimate that electrophoretic coatings have obvious advantages in coastal provinces and areas with severe acid rain in southern China. Referring to the market share of Japanese ED membranes, China will have considerable room for development in the next 10 years.
2.4 Progress of Anodizing Technology It is well-known that high efficiency and energy saving are the goals. The anodizing process parameters have not changed for decades. The sulfuric acid concentration and aluminum ion range, temperature and current density of solutions have been listed in the national standards. In order to improve the anodic oxidation efficiency and accelerate the deposition rate, it is necessary to increase the current density as much as possible under the precondition of ensuring the performance of the oxide film, and to find ways to improve the film formation factor. The thickness of the oxide film is proportional to the amount of coulomb passing (ie, the current multiplied by time) and varies from alloy to alloy. For example, for aluminum alloys 1100, 5005, 5052, and 6063, a 25 μm oxide film is required to produce 4700 bins/dm2; whereas 6061, 6082, and 6300 aluminum alloys require 5500 bins/dm2. At this time, if the applied current density is 1.5 A/dm2, the time required for the formation of a 20 [mu]m oxide film is 44 min, and the film formation rate is 0.46 [mu]m/min. The newly developed high-efficiency high-speed anodizing (HEA) filming speed in Italy can be increased to 1.2μm/min or more, and it is said that the current density can be stably operated at 3A/dm2 at 25°C. HEA technology is a whole design, including chemical, physical and mechanical cooperation. Chemical factors include the introduction of solution components and additives; physical factors include stirring methods, cooling systems, and combinations of solution temperature and current density; mechanical factors refer to multifunctional computer-controlled rectifiers, in which anodizing process computer (APC) devices are useful. .
2.5 Multi-color has always been the goal of coloring The electrolytic coloring of aluminum anodized film, the color is monotonous bronze, and seeking 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 a color is very troublesome for a trough, compound coloring can not escape the above difficulties, and has not achieved large-scale industrial 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 documents, 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. The authors worked on Italtecno's pilot line in Italia, under the guidance of DrStrazz, and visited the production line near Copenhagen, Denmark, and the Japan Showa Steel Machine Factory three times of electrolysis workshop. They also examined the Japan Seibu Department Store and the Copenhagen Airport. The application of the No. 3 door has proved that the colors are the same, there is no obvious color difference, and it breaks through the bronze frame and has a unique decorative effect. China's Zhejiang Dongliang Aluminum introduced Italian technology and equipment. On the basis of the original anodizing and electrolytic coloring of the plant, the Italian equipment was added to the previous production of multi-colored aluminum in April 2001, with uniform color and good repeatability. , Convenient control, has reached the requirements of mass production. Although this technology has strict requirements for the control of raw materials and anodizing processes, it is not an unsurpassable and unsurpassable technology. The commencement of multi-coloring of Dongliang Aluminum and its promotion in the future can change the monotonous situation of the traditional bronze and enable the construction industry to obtain more color options for aluminum profiles.
2.6 Improvement of the ecological environment is the development direction of the sealing process. There are many methods for sealing the aluminum oxide film. China is familiar with heat sealing holes, ED films and cold sealing holes, especially for cold sealing holes, but Ni2+ and F are more common. The pollution can not be ignored. Europe has conducted a series of studies for ecological considerations. First, it developed nickel-based fluoride-free medium-temperature sealed pores, and then developed nickel-free and fluorine-free medium-temperature sealed pores. Even metal ion-free medium temperature sealed pores are worthy of our reference. It may also become the direction of future development in China. The brief introduction is as follows:
2.6.1 Nickel based fluorine-free medium-temperature sealing nickel base (nickel acetate is suitable) can improve the quality of the sealing hole and stabilize the organic dye molecules in the film pores. The typical solution is:
NiAC 3~4g/L (without fluorine)
Anti-gray agent 100mg/L
Temperature 75～85°C
Sealing time 1~2min/μm
Or Ni2+0.4~1.1g/L
F-30～90mg/L (low fluorine)
Wetting agent 0.2 ~ 0.6mg/L
Ash suppressant 10 ~ 40mg/L
Temperature 75°C
Sealing time 0.5min/μm
2.6.2 Nickel-free and fluorine-free sealing It is recommended to replace nickel ions such as magnesium, lithium and potassium with alkali metals or alkaline earth metals. Sealing temperature 75 °C, pH 6.3, sealing time 1 ~ 2min / μm operation. Industrial practice shows that the quality of the sealing hole can be tested by international standards, and the bath life and energy saving effects are all satisfactory.
In addition, cold sealing of titanium and zirconium salts is also recommended. Because there is no toxicity, the quality of the sealing pores has reached a mass loss of 10 mg/dm2 of phosphoric acid, and the operating conditions are as follows:
Titanium or zirconium fluoride complex 3-10 g/L Silicate> 0.5 g/L Thiourea> 5 g/L Temperature 25-35°C Sealing time 0.5-1.0 min/μm
2.6.3 No Metallic Ion Temperature Sealed Clariant recently introduced a formulation that does not contain large amounts of metal ions. Further research is still under way and it will take time to expand applications.
In view of the ecological environment, the author believes that the non-nickel and fluorine-free medium and normal temperature sealing will be developed. The fluorine-free nickel-based medium temperature sealing process has been approved by European Qualanod, and is used in Europe and the United States. China can actively promote it.
2.7 Development of new technologies There are many new technologies in research, some of which may be close to the commercialization stage, while others only stay in the laboratory stage. One of the developments of the new technology is that Japan used the periodic reverse current technology to perform electrolytic etching in anodized sulfuric acid solution to remove extrusion striations. Although this 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 anodized colorings, two colors of pattern decoration effects are obtained. The aluminum plates used as interior decoration are unique and creative, and New Zealand calls it Aluart, 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.
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