Use of metal aluminum powder

Aluminum powder is a kind of metal pigment because of its wide use, large demand and variety The aluminum powder used for pigment is scaly, which is the reason why aluminum powder has the function of metal color and shielding Aluminum metal powder has been industrialized for a long time The early production method was ramming The aluminum chips were placed in the grooves of the rammer, and the rammer was driven by the machine to continuously punch the aluminum chips in the grooves The malleable aluminum gradually became thin and broken under the impact After the aluminum became very thin and small, it was screened, and the qualified aluminum powder was taken as the product The production efficiency of ramming method is very low, the product quality is not easy to master, and there is a lot of dust in the production process, which is very easy to fire and explode In 1894, hamtag, Germany, used a grinding mill to produce aluminum powder, put steel balls, aluminum scraps and lubricants in the ball mill, smashed aluminum scraps with flying steel balls, and then became flake aluminum powder, which was filled with inert gas in the ball mill and pipes This method is still in use, known as "dry production" In 1910, J Hall of the United States invented to replace inert gas with petroleum solvent in the ball mill, and the aluminum powder produced was mixed with the solvent to form a paste like aluminum powder pigment This method is simple in equipment, safe in process and convenient in use It has been adopted by many countries in the world Most of the modern aluminum pigments use this method, which is also called "wet method" China's aluminum powder industry started in the 1950s and has a history of 50 years The subsonic air atomization method of atomizing aluminum powder has been adopted, and the pressurized water atomization method has begun to enter the production sequence The products have both irregular shape and positive spherical shape In the production of aluminum powder and slurry by ball milling, both the dry process and the wet process are adopted by manufacturers The products are floating aluminum powder and aluminum slurry, non floating aluminum powder and aluminum slurry Water dispersive aluminum paste suitable for water-based coating has been produced for a long time Aluminum powder paste in the form of alloy, such as zinc aluminum paste, is also produced Properties and classification of aluminum powder and aluminum powder (I) characteristics of aluminum powder: aluminum is silver gray metal, with a relative mass of 26.98, a relative density of 2.55, a purity of 99.5% and a melting point of 685 degrees, a boiling point of 2065 degrees, and a melting latent heat of 323kj / G aluminum is reductive, easy to oxidize, and exothermic in the oxidation process In case of rapid oxidation, the heat release per gram is 15.5 kJ / g aluminum is a ductile metal and easy to process The oxide film on the surface of aluminum is transparent and has good chemical stability The aluminum powder used for pigment refers to the aluminum powder with scaly particles, surface coating agent and suitable for pigment Aluminum slurry is a mixture of pigment aluminum powder and solvent Its use and characteristics are roughly the same as aluminum powder Because it is easy to use, its output and consumption are larger (2) compared with other pigments, aluminum powder for pigment has its own characteristics, which are shown in the following aspects: 1 The characteristic of scale covering Aluminum powder particles are scaly, and the ratio of diameter to thickness is about (40:1) - (100:1) After being dispersed into the carrier, aluminum powder has the characteristics of being parallel to the substrate Many aluminum powder are connected with each other, and the size particles fill each other to form a continuous metal film, covering the substrate and reflecting the light outside the film, which is the unique covering power of aluminum powder The covering force of aluminum powder depends on the surface area, that is, the diameter thickness ratio Aluminum is extended in the grinding process, the diameter thickness ratio is increasing, and the covering power is also increasing 2 The shielding characteristics of aluminum powder dispersed in the carrier float, the result of which always makes itself parallel to the substrate coated by the carrier, forming a continuous aluminum powder layer, and the aluminum powder layer is arranged in parallel within the carrier film The pores of each layer of aluminum powder are staggered, which cut off the capillary pores of the carrier membrane The external water and gas can not reach the substrate through the pores, which is characterized by good physical shielding of aluminum powder 3 Optical characteristics of aluminum powder: aluminum powder is made of aluminum with light color and high metallic luster Its surface is bright and clean, which can reflect 60% - 90% of visible light, ultraviolet light and infrared light When coating objects with paint containing aluminum powder, its surface is silver white and bright, which is the feature of aluminum powder reflecting light 4 The "two color effect" characteristic of aluminum powder due to its metallic luster and parallel to the coating, in the carrier containing transparent pigment, the glossiness and color depth of aluminum powder change with the change of incident angle and angle of view of incident light, which is called "two color effect" The aluminum powder is arranged in different layers in the film When the incident light hits each layer of aluminum scale, the reflected light is obviously different because the film passing through different thickness is weakened differently When the light is injected into the film containing transparent pigment and aluminum powder, the incident light becomes colored light through the pigment particles, and then it is reflected out through different layers of aluminum powder, and the color and metal light will change The incident light and angle of view gradually shift from vertical, and the light passes through the pigments of different particle numbers and aluminum powder of different particle sizes, and the color and metal of the reflected light Light also changes infinitely This characteristic of aluminum powder has been widely used in paint as hammer paint or metal paint 5 The floating characteristics of aluminum powder a large type of aluminum powder and aluminum powder slurry for pigment is floating type, which is characterized by scale floating on the surface of the coating Application of aluminum powder I aluminum powder is commonly known as aluminum silver powder or silver powder due to its silver white metallic luster Its chemical composition is actually "aluminum", not "silver" Application scope: powder coating, ink, plastic masterbatch, printing, imitation gold paper, imitation gold card, gold film, textiles, but it will be oxidized and blackened when used in waterborne paint and paint with acid and alkali It is not recommended for applications requiring acid and alkali resistance and combination with rainwater   2 Ultra fine silver powder: 1 The surface area of ultra-fine floating silver is large When it is exposed to the air, it can quickly form a blunt protective film on its surface, i.e oxidation and blackening Sealing measures should be taken Floating silver is not recommended to be used in alkali resistant occasions If required, silver pearl powder can be considered; 2 There are certain differences between batches of silver powder and it is greatly affected by process and spraying, In addition to maintaining the stability of the production process as much as possible, the test should be carried out before production to avoid the expansion of losses 3 When adding 1-2% of ultra-fine silver to the bottom, 0.6% - 1.5% of ultra-fine silver can cover the bottom and produce a strong metallic luster when adding aw500b The larger the amount of silver powder is, the smaller the amount of silver powder is, the bluer it will be When the amount of silver powder is insufficient, there will be black spots and black silk, or commonly known as fly dung, which is generally black 4 Floating silver is flaky and always floats on the outermost layer of the coating, so the hardness and anti-oxidation blackening performance are slightly poor In order to obtain better hardness, it is necessary to add anti printing hardening agent as501 and silver powder hardening agent pol16pol09, etc the longer the mixing time, the better the effect is 3 Floating silver: 1 The smaller the size of silver powder, the stronger the metal sense, and the stronger the covering power; if the amount of silver powder is too large, it is easy to spit out powder and block the gun head; if the amount of silver powder is not enough, it is easy to appear black spots, flowers or small stripes R18, R01 and other special new silver powder dispersants are high-efficiency dispersants with SiO2 as the carrier Different from ordinary silver powder dispersants, no matter how much silver powder is added, it can be evenly dispersed without black spots Therefore, the effect of gray black, blue phase and different color phases of silver powder can be modulated by adjusting the background color and reducing the amount of silver powder The addition amount is very small, which has a good promoting effect on convective leveling When it is added to the sheet material for grinding together, it can not be directly added If it is directly added to the sheet material, it will produce the best R01 effect, such as grain material and white spot It is directly dry mixed without particles 2 The flake structure of floating aluminum powder will be destroyed (deformed or crushed) in the process of grinding and extrusion, resulting in gray color, so the dry mixing method is generally used 4 Non floating silver: 1 The non floating silver is evenly and parallel distributed in the whole coating film, so it is wrapped by resin, so it has good oxidation resistance and wear resistance, good weather resistance, acid resistance, alkali resistance, no hand print surface luster, and the color can be adjusted from the bottom powder, but the addition amount of large floating silver metal has no floating silver strong, white 2 PCR \ dis aluminum powder is especially suitable for outdoor products because of its inorganic coating, which has good water resistance, weather resistance and chemical resistance; although it is coated with silicon and other materials, in the environment of natural exposure, aluminum powder will soon undergo chemical and physical changes such as oxidation under the conditions of light, humidity and other conditions, so as to weaken the metal sense and make the film gray, dark and gray In order to solve these problems, it is suggested to use transparent powder to cover the surface 3 The amount of silver flash can be up to about 10% when the transparent powder is used as the test base The mixing and spraying process directly affects the spraying and covering effect Please pay attention to the uniformity of mixing and the coarser the spraying particle size, the better the flashing effect 4 Due to the difference between silver powder and powder in shape, density and charged quantity, the separation phenomenon will be caused and the powder will be affected Bonding the powder with silver powder by bonding technology can greatly improve the powder loading and effect 5 Aluminum powder can withstand high temperature 600 degrees without discoloration Safety precautions for the use of aluminum powder I General introduction: the safety risk of powder coating is lower than that of ordinary paint Compared with solvent / air mixture, the ignition energy of powder / air mixture is 50-100 times However, all combustible powder or dust will form explosive mixture with air, which is a potential hazard source However, if appropriate measures are taken in advance, safe transportation, storage and processing can be carried out For the sake of safety, the powder concentration of various powders mentioned above shall not exceed 10g / m3 In the spraying area, the concentration is often exceeded Because there is always enough oxygen content, it is necessary to avoid sparks that cause more than this minimum energy PTB BAM (Federal Laboratory of material testing) has measured the explosion data of various powder coatings containing pigments The results show that there is no difference between extruded and dry mixed materials in terms of "maximum explosion pressure" and "maximum increase pressure" Compared with the resin powder without pigment, when adding 5-6% aluminum powder, the so-called powder constant (the measure of burst force) and the maximum explosion pressure increase by 10% When the content of aluminum powder continues to increase, the explosive force will also increase When the content of aluminum powder is more than 25%, the explosive force of pure metal powder will be achieved However, this dependence on aluminum pigments is not intended to be used as the lowest initiating combustion energy No matter what kind of dispersion method is adopted, the pure resin powder can not reach the minimum ignition energy If the pigment content of aluminum powder is more than 10% and the aluminum powder with small particle size and without coating treatment is used, the lowest ignition energy may be reduced Powder coating containing aluminum powder, like ordinary powder coating containing pigment, has no danger of fire and explosion as long as it does not exceed the specified limit In order to ensure the safety of the whole spraying process, the separation, accumulation and concentration of aluminum powder in the factory must be avoided These basic requirements are also applicable to solvent coatings containing copper and gold powder However, the explosion risk caused directly by Cu Zn alloy powder is smaller than that caused by aluminum powder The most important parts and operation of powder equipment