Aluminum powder is a large class of metallic pigments due to its wide application, large demand, and large variety. The aluminum powder particles used for pigments are scale-like, and it is precisely because of the scale-like particle state that aluminum powder has metallic color and shielding functions. The industrial production of metal aluminum powder had existed for a long time ago. The early production method was the ramming process. Aluminum swarf was placed in the groove of the ramming machine, and the aluminum swarf in the groove was continuously punched by the machine. The ductile aluminum gradually becomes thin and breaks under impact, and after the aluminum becomes very thin and fine, it is screened and the desired aluminum powder is taken out as a product. The production efficiency of æ£Chong Chong method is very low, the product quality is not easy to grasp, and there are many dusts in the production process and it is very easy to catch fire and explode. In 1894, German Hamtag used a grinding machine to produce aluminum powder. Balls, aluminum chips and lubricants were put into the ball mill. After the aluminum balls were broken by the flying steel balls, they became scale-like aluminum powder. Inside the ball mill and in the pipeline Filled with inert gas, this method is still used, called "dry production." In 1910, the United States J.Hall invented the addition of petroleum solvent in the ball mill instead of inert gas, and the aluminum powder produced was mixed with a solvent to form a paste-like aluminum powder pigment. This method is simple in equipment, safe in process, and very convenient to use. It is quickly adopted by various countries in the world. Most modern aluminum powder pigments use this method. This method is also called “wet methodâ€.
The Chinese aluminum powder industry started in the 1950s and has a history of 50 years. The subsonic air atomization method of atomized aluminum powder has been adopted, and the pressurized water atomization method has also begun to enter the production sequence. The product has both irregular shape and positive spherical shape. In the ball mill method for manufacturing aluminum powder and aluminum slurry, dry and wet processes are used by manufacturers. The products produced are floating aluminum powder and aluminum slurry, non-leafing aluminum powder and aluminum slurry. Water-dispersed aluminum pastes suitable for water-based paints have been available for a long time, and aluminum pastes such as zinc-aluminum pastes in the form of alloys have also been produced.
Aluminum powder and aluminum slurry properties and classification
(A) The characteristics of aluminum powder
Aluminum is a silver-gray metal with a relative mass of 26.98, a relative density of 2.55, an aluminum purity of 99.5%, a melting point of 685 degrees, a boiling point of 2065 degrees, and a latent heat of fusion of 323 kj/g. Aluminum is reducible, easily oxidized, and released during oxidation. heat. With a rapid oxidation of 15.5 kj/g per gram, aluminum is a ductile metal that is easy to process. The aluminum oxide film on the surface is transparent and has good chemical stability.
The aluminum powder used for pigments refers to aluminum powder whose particles are flaky, coated with a surface treatment agent and suitable for pigments. Aluminum paste is a mixture of pigment aluminum powder and solvent. Its use and characteristics are almost the same as those of aluminum powder. Because it is easy to use, the output and dosage are greater.
(b) Compared with other pigments, aluminum powders for pigments have their own characteristics, which are manifested in the following aspects:
1, the characteristics of scaly covering aluminum particles are scale-like, the ratio of its diameter and thickness of about (40:1) - (100:1), aluminum powder dispersed into the carrier with the characteristics of the substrate parallel, many The aluminum powders are connected to each other, and the size particles fill each other to form a continuous metal film covering the substrate and reflecting the light outside the coating. This is the unique hiding power of aluminum powder. Aluminum powder hiding power depends on the size of the surface area, which is the ratio of diameter to thickness. Aluminum is extended during the grinding process, the ratio of diameter to thickness increases, and the hiding power increases.
2. Shielding properties of aluminum powder The aluminum powder dispersed in the carrier undergoes a floating motion. The result of its movement always makes itself parallel to the substrate coated by the carrier to form a continuous aluminum powder layer, and the aluminum powder layer is The carrier membranes are arranged in parallel within layers. The pores between the layers of aluminum powder are staggered with each other, and the capillary pores of the carrier film are cut off. External moisture and gas cannot pass through the pores to reach the substrate. This feature is good physical shielding of the aluminum powder.
3, the optical properties of aluminum powder Aluminum powder is made of light color, high metallic luster aluminum, its surface is smooth, can reflect 60% -90% of visible light, ultraviolet light and infrared light, coating with aluminum powder coating The surface of the object is silver-white and bright, which is the characteristic of aluminum powder reflecting light.
4, "two-color effect" characteristics of aluminum powder Aluminum powder due to the characteristics of metallic luster and parallel to the object to be coated, in the carrier containing transparent pigment, the degree of gloss and color of aluminum powder with the incident angle of incidence and perspective Changes occur in light and color changes. This characteristic is called "dual color effect." The aluminum powder is arranged in different layers within the coating film. When the incident light is irradiated to the aluminum flakes of various layers, the coating film subjected to different thicknesses is subjected to different weakening, and the reflected light clearly has different brightness. When light enters the film containing transparent pigments and aluminum powder, the incident light passes through the pigment particles and becomes colored light. After being reflected by different levels of aluminum powder, hue and metal light changes occur, incident light and viewing angle. Gradual movement of the angular position occurs perpendicularly, and light passes through pigments of different particle sizes and aluminum powders of different particle sizes. The color tone of the reflected light and metal light also undergo infinite changes. This property of aluminum powder has been widely used in paints as a hammer paint or metallic paint.
5, the floating characteristics of aluminum powder A large variety of aluminum powder and aluminum slurry for pigments is a floating type, which is characterized by scale-like floating on the surface of the coating.
Section III Application of Aluminum Powder
First, aluminum powder because of its silver-white metallic luster, so commonly known as aluminum silver powder or silver powder, its chemical composition is actually "aluminum", not "silver." Applications: powder coatings, inks, plastic masterbatches, printing, imitation gold paper, imitation gold cards, gold films, textiles, but in the use of water-based paint and paint with acid and alkali will be oxidized black. Not recommended for applications requiring acid and alkali combined with rain.
Second, ultra-fine silver powder: 1, ultra-fine floating silver surface area, when exposed to the air, can quickly generate a passive layer of protective film on the surface, that oxidation black, need to do a good sealing measures, floating silver is not Recommended for applications where alkali resistance is required. If required, silver white pearl powder may be considered. 2. Batches of silver powder have certain differences, and are affected by the process and spray. Except the need to maintain the stability of the production process. In addition, trial production should be conducted first to avoid increasing losses. 3, ultra-fine silver cover at the end of the amount of 1-2%, in the case of the addition of high light wax AW500B 0.6%-1.5% can cover the end and produce a strong metallic luster, the amount of silver powder is added, the more white, the smaller the amount of addition Blue, dark spots when the amount of added black silk, or commonly known as flies, the overall dark side. 4, floating silver is flake, always floating in the outermost layer of the coating, so the hardness and anti-oxidation black performance slightly worse, to get better hardness need to add printing India hardener AS501, plus silver powder Hard agent POL16, POL09, etc., can not add high wax, gold and silver powder arranging agent, polyethylene wax, etc. The longer the mixing time, the better the effect.
Third, floating silver: 1, the smaller the silver particle size, the stronger the sense of metal, the stronger the hiding power; the amount of addition is too easy to produce the phenomenon of spit powder and plug the gun; when the amount is not enough to easily appear black spots, hair or small Stripes. R18, R01 and other special effects of silver dispersant is SIO2 as a carrier of high-performance dispersant, different from the ordinary silver powder dispersant, no matter how much silver powder can be added evenly dispersed no black spots, so you can adjust the background color and reduce the amount of silver powder It can modulate the effect of silver powder in the black, blue and different hue. The addition amount is very small and it has a good promoting effect on the leveling. Except adding to the flake, it can not be added directly. It will produce particles and white spots directly. R01 has the best effect and it can dry and mix with no particles. 2. The sheet-like structure of the floated aluminum powder is destroyed (deformed or crushed) during the grinding and extrusion process. As a result, the color is grayed out, so the dry blending method is generally used.
Fourth, non-floating silver: 1, non-floating silver evenly distributed in the entire coating film in the middle, so it is wrapped in resin, so it has good oxidation resistance and abrasion resistance, better weathering acid and alkali resistance, No fingerprints, surface gloss, and the color can be adjusted from the bottom of the powder, but the amount of addition is larger than the floating silver, the metal effect is not floating silver strong, white. 2, PCR \ DIS aluminum powder is particularly suitable for outdoor products, because of inorganic coating, has good water resistance, weather resistance, chemical resistance; Although coated with silicon and other materials, but in the natural exposure of the environment, aluminum Powder under the conditions of light and humidity, oxidation and other chemical and physical changes will soon occur, so that the metal sensation weakened, the coating gray and dark, gray spots and so on. In order to solve such problems and scratches, it is recommended to use transparent powder covering. 3, the amount of the bottom cover with transparent base powder test, flash silver can add up to about 10%; mixing and spraying process directly affect the spraying and covering effect, please pay attention to the uniformity and consistency of the spraying, the coarser particle size The better the effect. 4. Since the silver powder particles differ in shape, density, and charge amount from the powder, separation phenomenon may be caused to affect the powder. Bonding technology is used to bond powder and silver powder, and the powder and effect are greatly improved. 5, aluminum powder can withstand high temperature 600 degrees do not change color.
Section 4 Safety Matters of Aluminum Powder Usage
First, general introduction
Powder coatings have a lower safety risk than ordinary paints. Compared to solvent/air mixtures, powder/air mixtures have a 50–100 times higher ignition energy. However, all flammable powders or dusts form an explosive mixture with air, which is a potential source of danger. However, if appropriate measures are taken in advance, safe transportation, storage and processing can be carried out. For safety reasons, the powder concentrations of the various powders mentioned above should not exceed 10 g/m3. In the spray area, this concentration is often exceeded. Because there is always enough oxygen, sparks that exceed this minimum energy must be avoided.
PTB (Federal Institute of Physical Technology) BAM (Federal Laboratories for Materials Testing) has determined explosion data for various pigmented powder coatings. The results demonstrate that there is no difference between the extruded and dry blended materials in terms of "highest explosive pressure" and "maximum increased pressure."
Compared with non-pigmented resin powders, the so-called powder constant (Dust Comstant) and maximum explosion pressure increase by 10% when 5-6% aluminum powder is added. As the aluminum powder content continues to increase, the explosive force increases. When the aluminum powder content is greater than 25%, the explosive power of the pure metal powder is reached. However, this dependence on aluminum powder pigments is not intended to be used for the lowest ignition energy. Regardless of the dispersion method used, the pure resin powder does not reach the minimum ignition energy. If the content of aluminum powder pigment is >10% and the use of fine-grained and uncoated aluminum powder, the lowest ignition energy may be reduced.
Powder coatings containing aluminum powder, like normal pigmented powder coatings, do not ignite or explode unless they exceed the specified limits.
In order to ensure the safety during the entire spraying process, the separation, accumulation and concentration of aluminum powder in the factory must be avoided. These basic requirements also apply to solvent-based coatings containing copper gold powder. However, the risk of explosion caused by copper-zinc alloy powder is smaller than that of aluminum powder.
The most important thing for powder equipment is that all components and operators must have good grounding. The indoor dust concentration should be controlled to the lowest level, and the exhaust system should be used according to local regulations. In any case, avoid open flames, sparks and hot surfaces.
Section 5 Production and Processing Methods of Aluminum Powder
1, melt extrusion method:
In this method, the metal pigment and the remaining components of the powder coating (resin, etc.) are heated and extruded through a screw extruder. Although the metal pigment and the powder coating can be sufficiently mixed, the metal pigment is insufficiently oriented in the high-viscosity melt. In addition, in the next crushing process, the sheet structure of the pigment is inevitably destroyed. The metal powder produced by this method has a gray metallic effect during construction. Therefore, this method is only used for the production of hammer powder.
2, dry mixing method:
The method is to add the dry powder of metal pigment into the crushed powder coating and mix it with a mechanical mixer. The advantage of the dry blending method is that the metal pigment and the powder coating are not very intense when mixed, thereby preventing the deformation of the sheet metal pigment and the metal effect is not affected either. In addition, loose pigment/resin blends are also very beneficial to the orientation of metallic pigments and improve the glittering effect. The disadvantage of this method is that when an automatic spray apparatus is used to treat the recovered powder, the separation phenomenon occurs due to the large difference in shape, density, and charged charge between the metal pigment and the resin powder particles.
3. Bonding-Process:
In this method, the metallic pigment and the powder coating are dry-blended while being heated at the same time so that the temperature just exceeds the softening point of the resin. At this point, the metallic pigment can be fixed and adhered to the surface of the viscous resin powder, thereby preventing the powder from being applied. The separation of metal pigments from resin powders after recovery from neutralization. It is now the popular law of bonding.
The Chinese aluminum powder industry started in the 1950s and has a history of 50 years. The subsonic air atomization method of atomized aluminum powder has been adopted, and the pressurized water atomization method has also begun to enter the production sequence. The product has both irregular shape and positive spherical shape. In the ball mill method for manufacturing aluminum powder and aluminum slurry, dry and wet processes are used by manufacturers. The products produced are floating aluminum powder and aluminum slurry, non-leafing aluminum powder and aluminum slurry. Water-dispersed aluminum pastes suitable for water-based paints have been available for a long time, and aluminum pastes such as zinc-aluminum pastes in the form of alloys have also been produced.
Aluminum powder and aluminum slurry properties and classification
(A) The characteristics of aluminum powder
Aluminum is a silver-gray metal with a relative mass of 26.98, a relative density of 2.55, an aluminum purity of 99.5%, a melting point of 685 degrees, a boiling point of 2065 degrees, and a latent heat of fusion of 323 kj/g. Aluminum is reducible, easily oxidized, and released during oxidation. heat. With a rapid oxidation of 15.5 kj/g per gram, aluminum is a ductile metal that is easy to process. The aluminum oxide film on the surface is transparent and has good chemical stability.
The aluminum powder used for pigments refers to aluminum powder whose particles are flaky, coated with a surface treatment agent and suitable for pigments. Aluminum paste is a mixture of pigment aluminum powder and solvent. Its use and characteristics are almost the same as those of aluminum powder. Because it is easy to use, the output and dosage are greater.
(b) Compared with other pigments, aluminum powders for pigments have their own characteristics, which are manifested in the following aspects:
1, the characteristics of scaly covering aluminum particles are scale-like, the ratio of its diameter and thickness of about (40:1) - (100:1), aluminum powder dispersed into the carrier with the characteristics of the substrate parallel, many The aluminum powders are connected to each other, and the size particles fill each other to form a continuous metal film covering the substrate and reflecting the light outside the coating. This is the unique hiding power of aluminum powder. Aluminum powder hiding power depends on the size of the surface area, which is the ratio of diameter to thickness. Aluminum is extended during the grinding process, the ratio of diameter to thickness increases, and the hiding power increases.
2. Shielding properties of aluminum powder The aluminum powder dispersed in the carrier undergoes a floating motion. The result of its movement always makes itself parallel to the substrate coated by the carrier to form a continuous aluminum powder layer, and the aluminum powder layer is The carrier membranes are arranged in parallel within layers. The pores between the layers of aluminum powder are staggered with each other, and the capillary pores of the carrier film are cut off. External moisture and gas cannot pass through the pores to reach the substrate. This feature is good physical shielding of the aluminum powder.
3, the optical properties of aluminum powder Aluminum powder is made of light color, high metallic luster aluminum, its surface is smooth, can reflect 60% -90% of visible light, ultraviolet light and infrared light, coating with aluminum powder coating The surface of the object is silver-white and bright, which is the characteristic of aluminum powder reflecting light.
4, "two-color effect" characteristics of aluminum powder Aluminum powder due to the characteristics of metallic luster and parallel to the object to be coated, in the carrier containing transparent pigment, the degree of gloss and color of aluminum powder with the incident angle of incidence and perspective Changes occur in light and color changes. This characteristic is called "dual color effect." The aluminum powder is arranged in different layers within the coating film. When the incident light is irradiated to the aluminum flakes of various layers, the coating film subjected to different thicknesses is subjected to different weakening, and the reflected light clearly has different brightness. When light enters the film containing transparent pigments and aluminum powder, the incident light passes through the pigment particles and becomes colored light. After being reflected by different levels of aluminum powder, hue and metal light changes occur, incident light and viewing angle. Gradual movement of the angular position occurs perpendicularly, and light passes through pigments of different particle sizes and aluminum powders of different particle sizes. The color tone of the reflected light and metal light also undergo infinite changes. This property of aluminum powder has been widely used in paints as a hammer paint or metallic paint.
5, the floating characteristics of aluminum powder A large variety of aluminum powder and aluminum slurry for pigments is a floating type, which is characterized by scale-like floating on the surface of the coating.
Section III Application of Aluminum Powder
First, aluminum powder because of its silver-white metallic luster, so commonly known as aluminum silver powder or silver powder, its chemical composition is actually "aluminum", not "silver." Applications: powder coatings, inks, plastic masterbatches, printing, imitation gold paper, imitation gold cards, gold films, textiles, but in the use of water-based paint and paint with acid and alkali will be oxidized black. Not recommended for applications requiring acid and alkali combined with rain.
Second, ultra-fine silver powder: 1, ultra-fine floating silver surface area, when exposed to the air, can quickly generate a passive layer of protective film on the surface, that oxidation black, need to do a good sealing measures, floating silver is not Recommended for applications where alkali resistance is required. If required, silver white pearl powder may be considered. 2. Batches of silver powder have certain differences, and are affected by the process and spray. Except the need to maintain the stability of the production process. In addition, trial production should be conducted first to avoid increasing losses. 3, ultra-fine silver cover at the end of the amount of 1-2%, in the case of the addition of high light wax AW500B 0.6%-1.5% can cover the end and produce a strong metallic luster, the amount of silver powder is added, the more white, the smaller the amount of addition Blue, dark spots when the amount of added black silk, or commonly known as flies, the overall dark side. 4, floating silver is flake, always floating in the outermost layer of the coating, so the hardness and anti-oxidation black performance slightly worse, to get better hardness need to add printing India hardener AS501, plus silver powder Hard agent POL16, POL09, etc., can not add high wax, gold and silver powder arranging agent, polyethylene wax, etc. The longer the mixing time, the better the effect.
Third, floating silver: 1, the smaller the silver particle size, the stronger the sense of metal, the stronger the hiding power; the amount of addition is too easy to produce the phenomenon of spit powder and plug the gun; when the amount is not enough to easily appear black spots, hair or small Stripes. R18, R01 and other special effects of silver dispersant is SIO2 as a carrier of high-performance dispersant, different from the ordinary silver powder dispersant, no matter how much silver powder can be added evenly dispersed no black spots, so you can adjust the background color and reduce the amount of silver powder It can modulate the effect of silver powder in the black, blue and different hue. The addition amount is very small and it has a good promoting effect on the leveling. Except adding to the flake, it can not be added directly. It will produce particles and white spots directly. R01 has the best effect and it can dry and mix with no particles. 2. The sheet-like structure of the floated aluminum powder is destroyed (deformed or crushed) during the grinding and extrusion process. As a result, the color is grayed out, so the dry blending method is generally used.
Fourth, non-floating silver: 1, non-floating silver evenly distributed in the entire coating film in the middle, so it is wrapped in resin, so it has good oxidation resistance and abrasion resistance, better weathering acid and alkali resistance, No fingerprints, surface gloss, and the color can be adjusted from the bottom of the powder, but the amount of addition is larger than the floating silver, the metal effect is not floating silver strong, white. 2, PCR \ DIS aluminum powder is particularly suitable for outdoor products, because of inorganic coating, has good water resistance, weather resistance, chemical resistance; Although coated with silicon and other materials, but in the natural exposure of the environment, aluminum Powder under the conditions of light and humidity, oxidation and other chemical and physical changes will soon occur, so that the metal sensation weakened, the coating gray and dark, gray spots and so on. In order to solve such problems and scratches, it is recommended to use transparent powder covering. 3, the amount of the bottom cover with transparent base powder test, flash silver can add up to about 10%; mixing and spraying process directly affect the spraying and covering effect, please pay attention to the uniformity and consistency of the spraying, the coarser particle size The better the effect. 4. Since the silver powder particles differ in shape, density, and charge amount from the powder, separation phenomenon may be caused to affect the powder. Bonding technology is used to bond powder and silver powder, and the powder and effect are greatly improved. 5, aluminum powder can withstand high temperature 600 degrees do not change color.
Section 4 Safety Matters of Aluminum Powder Usage
First, general introduction
Powder coatings have a lower safety risk than ordinary paints. Compared to solvent/air mixtures, powder/air mixtures have a 50–100 times higher ignition energy. However, all flammable powders or dusts form an explosive mixture with air, which is a potential source of danger. However, if appropriate measures are taken in advance, safe transportation, storage and processing can be carried out. For safety reasons, the powder concentrations of the various powders mentioned above should not exceed 10 g/m3. In the spray area, this concentration is often exceeded. Because there is always enough oxygen, sparks that exceed this minimum energy must be avoided.
PTB (Federal Institute of Physical Technology) BAM (Federal Laboratories for Materials Testing) has determined explosion data for various pigmented powder coatings. The results demonstrate that there is no difference between the extruded and dry blended materials in terms of "highest explosive pressure" and "maximum increased pressure."
Compared with non-pigmented resin powders, the so-called powder constant (Dust Comstant) and maximum explosion pressure increase by 10% when 5-6% aluminum powder is added. As the aluminum powder content continues to increase, the explosive force increases. When the aluminum powder content is greater than 25%, the explosive power of the pure metal powder is reached. However, this dependence on aluminum powder pigments is not intended to be used for the lowest ignition energy. Regardless of the dispersion method used, the pure resin powder does not reach the minimum ignition energy. If the content of aluminum powder pigment is >10% and the use of fine-grained and uncoated aluminum powder, the lowest ignition energy may be reduced.
Powder coatings containing aluminum powder, like normal pigmented powder coatings, do not ignite or explode unless they exceed the specified limits.
In order to ensure the safety during the entire spraying process, the separation, accumulation and concentration of aluminum powder in the factory must be avoided. These basic requirements also apply to solvent-based coatings containing copper gold powder. However, the risk of explosion caused by copper-zinc alloy powder is smaller than that of aluminum powder.
The most important thing for powder equipment is that all components and operators must have good grounding. The indoor dust concentration should be controlled to the lowest level, and the exhaust system should be used according to local regulations. In any case, avoid open flames, sparks and hot surfaces.
Section 5 Production and Processing Methods of Aluminum Powder
1, melt extrusion method:
In this method, the metal pigment and the remaining components of the powder coating (resin, etc.) are heated and extruded through a screw extruder. Although the metal pigment and the powder coating can be sufficiently mixed, the metal pigment is insufficiently oriented in the high-viscosity melt. In addition, in the next crushing process, the sheet structure of the pigment is inevitably destroyed. The metal powder produced by this method has a gray metallic effect during construction. Therefore, this method is only used for the production of hammer powder.
2, dry mixing method:
The method is to add the dry powder of metal pigment into the crushed powder coating and mix it with a mechanical mixer. The advantage of the dry blending method is that the metal pigment and the powder coating are not very intense when mixed, thereby preventing the deformation of the sheet metal pigment and the metal effect is not affected either. In addition, loose pigment/resin blends are also very beneficial to the orientation of metallic pigments and improve the glittering effect. The disadvantage of this method is that when an automatic spray apparatus is used to treat the recovered powder, the separation phenomenon occurs due to the large difference in shape, density, and charged charge between the metal pigment and the resin powder particles.
3. Bonding-Process:
In this method, the metallic pigment and the powder coating are dry-blended while being heated at the same time so that the temperature just exceeds the softening point of the resin. At this point, the metallic pigment can be fixed and adhered to the surface of the viscous resin powder, thereby preventing the powder from being applied. The separation of metal pigments from resin powders after recovery from neutralization. It is now the popular law of bonding.
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