CN105086527A - Low-infrared-emissivity composite pigment and preparation method thereof - Google Patents

Abstract

The invention provides a low-infrared emissivity composite pigment and a preparation method thereof, comprising the following steps: using Bi(NO) ₃ 5H ₂ O as a solute, ethylene glycol as a solvent, preparing a bismuth nitrate solution, adding a dispersant, aluminum Powder, after ultrasonic dispersion, add weak base solution dropwise at a uniform speed; after the reaction is completed, collect the precipitate and dry it, grind it to obtain the precursor powder; calcinate the obtained precursor powder, and obtain a low infrared emissivity composite pigment after cooling with the furnace; the pigment is a surface The flaky aluminum powder pigment coated with bismuth oxide, the low-infrared emissivity composite structural pigment prepared by the method of the present invention has a yellow appearance and low metallic luster. Under the optimal formula and process conditions, the average emissivity in the infrared band is 0.43, It meets the technical requirements of color energy-saving coatings and camouflage applications; the color is yellow, the b* value is as high as 33.8, and the brightness is 65.8, which can be used for adjusting the optical properties of low-emissivity coatings; after calcination, it has good thermal stability; non-toxic, The preparation has little harm to the human body and no pollution to the environment.

Description

Composite pigment with low infrared emissivity and preparation method thereof

technical field

The invention belongs to the technical field of functional materials, and relates to energy-saving and environment-friendly coating material technology, in particular to a composite pigment with low infrared emissivity composed of flake aluminum powder and a bismuth oxide layer coated on its outside and a preparation method thereof.

Background technique

Low infrared emissivity coatings have low heat radiation and heat shielding functions, and have broad application prospects in many national economic fields such as thermal control, energy saving, stealth and camouflage. Low infrared radiation emissivity coatings are usually composed of infrared reflective pigments, coloring pigments and binders, wherein infrared reflective pigments are the main functional medium, carrying the high infrared reflection (low infrared radiation) function of the coating; metallic pigments are currently the most widely used Mature and common infrared reflective pigments, among which flake aluminum powder has become the first choice for low infrared emissivity coatings because of its low price and easy availability. Although aluminum powder pigments have excellent thermal infrared reflection characteristics, their high reflection characteristics will also cause high brightness and high reflection problems of the coating. Whether it is in the fields of energy saving, thermal control, or camouflage and other application backgrounds, it should be avoided as much as possible. ; The former will cause insufficient visual aesthetics and a certain degree of light pollution, while the latter will directly lead to the deterioration of multi-spectrum camouflage and stealth performance.

The researchers found that: aluminum powder is used as the core particle, and a layer of colored pigment particles is coated on the surface of the particle by chemical or physical means. The composite particle of this core-shell structure can usually combine the characteristics of the two particles, and even produce a core-shell structure. A property or function that particles do not have individually. US4328042 discloses a method for coating aluminum powder: a layer of iron oxide particles is deposited on the surface of aluminum powder by means of CVD to make a composite powder pigment. The composite pigment has a strong metallic luster, and by adjusting the thickness of the iron oxide coating layer, the powder presents different colors. However, the CVD method has expensive equipment and high production costs, and the products are mostly used in high-end car paints. Since then, there have been endless reports about coated aluminum powder. CN200810163113.8 discloses a preparation method of a 3-layer composite aluminum pigment: the composite pigment is composed of aluminum powder as the inner layer, silicon dioxide as the middle layer and metal oxide (ferric oxide or chromium oxide) as the outer shell constitute. The composite pigment has a high concentration and has a higher metallic luster; similar CN201210506950.2 also discloses a composite pigment composed of aluminum, silicon dioxide and ferric oxide, and the pigment can be used at a higher temperature (120° C. ) will not fade. The composite pigments in these two reports are composed of 3 kinds of materials (aluminum core, silica intermediate layer, metal oxide shell), with complex structure, complex production process and high cost. Since the silica interlayer has a strong ability to bind the hydroxyl groups on the surface of the aluminum sheet and the metal oxide, it can make the metal oxide coating layer stronger. In addition, the introduction of the silica interlayer can also enhance the color effect , but the introduction of the intermediate layer will lead to the complex structure of the aluminum pigment, the thickness of the cladding layer will increase, and the infrared emissivity of the pigment will deteriorate.

In addition, the method of liquid phase precipitation can also be used to directly coat a layer of metal oxide on the surface of the flake aluminum powder. This kind of composite pigment obtained by directly coating oxide particles on the surface of aluminum flakes by liquid phase precipitation method lacks the silica intermediate layer that plays a bonding role in the structure, so the bond between the oxide coating layer and the aluminum flakes is not as firm as A pigment with a silica layer, but its structure is simple, the coating layer is thin, and the infrared emissivity is very low; on the other hand, the preparation process is relatively simple and the cost is relatively low. Since the chemical properties of aluminum powder are very active, it is very easy to be oxidized by oxidizing agents or reduced by reducing agents, so when the aluminum powder is directly coated by the liquid phase method, the aluminum powder is very easy to be corroded. Therefore, it is extremely important to select a suitable liquid-phase reaction environment. At present, the liquid phase reaction environment can be divided into three types: water, alcohol and oil phase.

The research on the use of water phase reaction environment has been relatively mature. CN200510027121.6 discloses a surface-coated ferric oxide flake aluminum powder pigment with low emissivity in the infrared band and its preparation method. The pigment is brown, Dull, the average emissivity in the infrared band (8-14um) is 0.50-0.65, but the reaction temperature of this method is 65-98°C, and the aluminum powder is easily corroded by water. CN200510027124.X discloses a flaky aluminum pigment coated with ferric oxide hydrate on the surface and a preparation method thereof. The method has low reaction temperature (25-50° C.), mild reaction, khaki-yellow pigment, and an emissivity of 0.50-50°C. 0.60.CN201210443154.9 discloses a method for preparing aluminum composite particles coated with nano oxygen-carrying materials. At a reaction temperature of 80-100°C, the surface of aluminum powder is coated with chromium oxide, iron oxide, copper oxide, and nickel oxide respectively. , cobalt oxide and other oxides. The biggest advantage of the water-phase reaction environment is that water can dissolve a variety of metal salts, and it is cheap and easy to get. But water is easy to corrode aluminum powder, especially when the reaction system is heated above 60 degrees, the corrosion of water to aluminum powder is intensified.

In order to reduce the corrosion of the aluminum powder by the reaction environment, researchers use the alcohol phase reaction environment instead of the water phase environment. CN201210072246.0 discloses a low lightness and low emissivity aluminum pigment and its preparation method. The pigment is yellow-green, composed of aluminum Composed of a core and a chromium oxide shell, the emissivity in the infrared band (8-14um) is 0.43-0.70, and the brightness is 53.6-72.1. The method uses absolute ethanol to dissolve the chromium salt, which effectively reduces the corrosion of the aluminum powder. However, ethanol cannot dissolve some metal salts, such as bismuth nitrate, etc., so the ethanol environment cannot be used to coat bismuth oxide on aluminum sheets. In addition, chromium oxide is poisonous, easy to pollute the environment, and the preparation process is harmful to the human body.

There are few studies on the coating of aluminum powder in the oil phase. CN201410361019.9 discloses the method of using high-temperature oil phase to in-situ synthesize iron ferric oxide nanoparticles on the surface of flake aluminum particles, and obtain ferric iron tetroxide with magnetic properties. Nanoparticle/Flake Aluminum Pigment Composite Nanomaterials. However, the process of this method is complicated, and it needs to be stirred and reacted at 310-330° C. under nitrogen atmosphere, which has high requirements on the reaction device and high cost.

It can be seen that the currently used metal oxide coloring pigment particles are mostly ferric oxide, ferric oxide and chromium oxide. However, the infrared emissivity of these materials is relatively high, and some metal oxides are toxic and easy to pollute the environment. There are few reports on the use of bismuth oxide, which has a relatively low infrared emission rate and is non-toxic and environmentally friendly, as coated particles. Because in the water phase environment, not only the aluminum powder will be corroded, but also the bismuth salt is easily hydrolyzed, so it is difficult to use the water phase reaction environment to realize the coating of bismuth oxide on the aluminum sheet. In the oil phase reaction environment, the preparation process and reaction device are complicated and the cost is high. Relatively speaking, the reaction in the environment of alcohol solution is mild, and the corrosion degree of aluminum powder is low.

Contents of the invention

In view of the above-mentioned shortcomings of the prior art, the object of the present invention is to provide a color and environment-friendly low-infrared emissivity composite pigment and its preparation method, which are used to meet the demand for high-performance colored aluminum powder pigments.

In order to achieve the purpose of the above invention, the present invention provides a composite pigment with low infrared emissivity. The pigment is a flaky aluminum powder pigment coated with bismuth oxide on the surface. The coating thickness is 0.2um-0.6um, the brightness L* value of the pigment is 65-77, and the b* value of the color channel from blue to yellow is +2.8-+42.

The composite structural pigment is an aluminum powder coated with nano bismuth oxide particles on the surface, and the metallic luster on the surface of the aluminum powder is covered by the nano particles while improving the corrosion resistance of the aluminum powder without excessively reducing the high infrared reflection ability of the aluminum powder. A composite material with better compatible stealth performance in the visible light and infrared bands is obtained.

The present invention also provides a preparation method of the above-mentioned low infrared emissivity composite pigment, comprising the following steps:

(1) Add Bi(NO) _3． 5H ₂ O is used as the solute, ethylene glycol is used as the solvent, and a bismuth nitrate solution with a Bi ³⁺ concentration of 0.05-0.20 mol/L is prepared, and a dispersant and aluminum powder are added to it. The dispersant added to each liter of solvent is 0.5- 0.7g, the molar ratio of the solute and the aluminum powder is 0.1:1～0.4:1, and after ultrasonic dispersion, the alkaline solution is added dropwise at a uniform speed to make all the Bi ³⁺ in the reaction solution precipitate;

(2) Suction filtration after the reaction is completed, the filter residue is dried, and the precursor powder is obtained after grinding;

(3) Put the obtained precursor powder into a muffle furnace for calcination at 400-500° C. for 2-3 hours, and obtain a low-infrared emissivity composite pigment after cooling with the furnace.

The present invention selects bismuth nitrate as the bismuth salt that provides bismuth ions. Bismuth salts other than bismuth nitrate, such as bismuth chloride, will generate a bismuth oxychloride precursor when bismuth chloride encounters a weak base solution, and the expected product cannot be obtained. The Bi ³⁺ exists in the form of coordination ions, which cannot effectively provide Bi ³⁺ .

The molar ratio of the solute to the aluminum powder is 0.1:1 to 0.4:1. When the ratio of the aluminum powder to Bi(NO ₃ ) ₃ is too low, the surface area of the aluminum sheet available for coating is limited, and the finally obtained bismuth oxide particles are agglomerated Seriously, these agglomerates are either accumulated on the surface of the aluminum powder, or interspersed between the powders, making the emissivity of the powders rise sharply. When the ratio of aluminum powder to Bi(NO ₃ ) ₃ is too high, the Bi ³⁺ is too low to effectively form a uniform coating layer on the surface of the aluminum sheet, the coating layer is sparse, and the appearance color of the powder is light, although the emission of the powder The rate is very low, but the metallic luster is strong.

The calcination temperature should be controlled between 400 and 500 degrees. If the calcination temperature is lower than 400 degrees, the precursor cannot be completely converted into bismuth oxide; if the calcination temperature is higher than 500 degrees, the aluminum sheet will be oxidized or even deformed.

The choice of solvent needs to ensure that the bismuth nitrate can be completely dissolved in it and form a stable solution. In addition, the solvent cannot chemically react with aluminum. Commonly used solvents, such as water and ethanol, are not suitable as solvents in the present invention. Because Bi ³⁺ is easily hydrolyzed in water and cannot exist stably, water is easy to corrode aluminum powder under heating conditions; ethanol cannot be used because bismuth nitrate is difficult to dissolve in ethanol. In the invention, a suitable alcohol phase environment is selected so that the bismuth salt can be fully dissolved, and the aluminum pigment whose surface is coated with bismuth oxide nanoparticles is prepared at a mild reaction temperature.

As a preferred manner, the dispersant is sodium dodecyl sulfate or sodium dodecylbenzenesulfonate.

As a preferred mode, the aluminum powder added in the reaction is a non-leafing flake aluminum powder with concentrated particle size distribution, and the particle diameter of the non-leafing flake aluminum powder is 1-50 um.

As a preferred mode, after ultrasonic dispersion, a weak base solution with a pH value of 8-9 is added dropwise at a constant rate of 0.2-1.5 ml/min to precipitate all Bi ³⁺ in the reaction solution.

The higher the concentration of lye, the slower the rate of addition must be. A slower dropping rate can utilize the heterogeneous nucleation of the precursor to improve the coating effect on the aluminum sheet. Too fast dropping rate is not conducive to heterogeneous nucleation, resulting in poor coating effect. In addition, too fast dropping rate will also cause the local OH ^-1 concentration of the reaction solution to be too high, because the micron-sized flaky aluminum powder has high activity and will react with OH ^-1 . Therefore, it is advisable to keep the dropping rate at 0.2-1.5ml/min.

As a preferred manner, the alkaline solution is ammonia water or sodium hydroxide solution.

If the amount of alkali used is too low, the Bi ³⁺ in the above reaction solution cannot be completely precipitated, and if the amount used is too high, the corrosion of the aluminum powder will be aggravated. In order to ensure that all the Bi ³⁺ in the above reaction solution is precipitated, it is advisable to have a slight excess of weak base (pH value 8-9), not too much or too little.

As a preferred mode, the constant temperature of the reaction system in the step (1) is controlled at 30-60 degrees.

When adding the alkaline solution, the reaction system should be mixed and stirred at a constant temperature of 30-60 degrees. If the temperature is too low, the energy of the reaction system will be insufficient and the reaction will be slow; if the temperature is too high, the energy of the reaction system will be too high, the reaction rate will be accelerated and difficult to control, and the final coating effect will be poor. In addition, the high temperature will also aggravate the corrosion of aluminum powder. The stirring speed should be appropriate to ensure that the reaction system is evenly mixed. Too slow will cause uneven mixing and the aluminum flakes will sink to the bottom. Too fast stirring will cause droplets to splash.

The beneficial effects of the present invention are: the present invention provides a color and environment-friendly composite structure pigment with low infrared emissivity, which is used to meet the demand for high-performance colored aluminum powder pigment. The low-infrared emissivity composite structural pigment prepared by the method of the present invention has a yellow appearance and low metallic luster. Under the optimal formula and process conditions, the average emissivity in the infrared band (8-14um) is 0.43, which meets the requirements of infrared stealth. Requirements: The color is yellow, the b* value is as high as 33.8, and the brightness is 65.8. It can be used as a visible light camouflage filler; after calcination, it has good thermal stability; it is non-toxic, has little harm to the human body during preparation, and has no pollution to the environment.

Description of drawings

Fig. 1 is the electron micrograph of the pigment that the present invention makes.

Figure 2 is an electron micrograph of the original aluminum pigment.

Fig. 3 is the 8-14um infrared reflection characteristic curve of the pigment prepared by the present invention and the original aluminum powder.

Detailed ways

Embodiments of the present invention are described below through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific implementation modes, and various modifications or changes can be made to the details in this specification based on different viewpoints and applications without departing from the spirit of the present invention.

Example 1

(1) Add Bi(NO) _3． 5H ₂ O is used as the solute, ethylene glycol is used as the solvent, and a bismuth nitrate solution with a Bi ³⁺ concentration of 0.20 mol/L is prepared, and a dispersant and aluminum powder are added thereto, and the dispersant is sodium lauryl sulfate. The dispersant that adds in every liter of solvent is 0.5g, and the mol ratio of described solute and aluminum powder is 0.1:1, and the weak base solution that pH is 9 is added dropwise at a constant speed with the drip rate of 1.5ml/min after ultrasonic dispersion makes All Bi ³⁺ in the reaction liquid precipitates; the alkaline solution is ammonia water, and the constant temperature of the reaction system is controlled at 30 degrees.

(2) Suction filtration after the reaction is completed, the filter residue is dried, and the precursor powder is obtained after grinding;

(3) Put the obtained precursor powder into a muffle furnace for calcination at 400° C. for 2 h, and obtain a low-infrared emissivity composite pigment after cooling with the furnace.

The aluminum powder added in the reaction is a non-leafing flaky aluminum powder with a concentrated particle size distribution, and the particle size of the non-floating flaky aluminum powder is 1 μm.

The composite pigment with low infrared emissivity prepared by the above preparation method is a flaky aluminum powder pigment coated with bismuth oxide on the surface. um, the brightness L* value of the pigment is 75~77, and the b* value of the color channel from blue to yellow is +2.8~+5.0.

Example 2

(1) Add Bi(NO) _3． 5H O is as solute, and ethylene glycol is solvent, is mixed with the bismuth nitrate solution that Bi ³⁺ concentration is 0.05mol/L, adds dispersant, aluminum powder wherein, the dispersant that adds in every liter of solvent is 0.7g, described dispersant The agent is sodium lauryl sulfate. The molar ratio of the solute and the aluminum powder is 0.4:1, after ultrasonic dispersion, the weak base solution with a pH value of 9 is added dropwise at a uniform speed at a rate of 0.2ml/min to make the Bi in the reaction solution ³⁺ all precipitate; The alkaline solution is sodium hydroxide solution. In the step (1), the constant temperature of the reaction system is controlled at 60 degrees.

(2) Suction filtration after the reaction is completed, the filter residue is dried, and the precursor powder is obtained after grinding;

(3) Put the obtained precursor powder into a muffle furnace for calcination at 450° C. for 3 h, and obtain a low-infrared emissivity composite pigment after cooling with the furnace.

The aluminum powder added in the reaction is a non-leafing flaky aluminum powder with a concentrated particle size distribution, and the particle size of the non-floating flaky aluminum powder is 50 um.

The composite pigment with low infrared emissivity prepared by the above preparation method is a flaky aluminum powder pigment coated with bismuth oxide on the surface. um, the brightness L* value of the pigment is 66~68, and the b* value of the color channel from blue to yellow is +39~+42.

Example 3

(1) Add Bi(NO) _3． 5H ₂ O is as solute, ethylene glycol is solvent, is mixed with the bismuth nitrate solution that Bi ³⁺ concentration is 0.1mol/L, adds dispersant, aluminum powder wherein, the dispersant that adds in every liter of solvent is 0.6g, so The dispersant is sodium lauryl sulfate. The molar ratio of the solute and the aluminum powder is 0.2:1, after the ultrasonic dispersion, the weak base solution with a pH value of 8 is added dropwise at a uniform speed at a rate of 0.5ml/min to make the Bi in the reaction solution ³⁺ all precipitate; The alkaline solution is ammonia water. The temperature of the reaction system was controlled at 40°C.

(2) Suction filtration after the reaction is completed, the filter residue is dried, and the precursor powder is obtained after grinding;

(3) Put the obtained precursor powder into a muffle furnace for calcination at 400° C. for 2 h, and obtain a low-infrared emissivity composite pigment after cooling with the furnace.

The aluminum powder added in the reaction is non-leafing flake aluminum powder with concentrated particle size distribution, and the particle diameter of the non-leafing flake aluminum powder is 25um.

The low infrared emissivity composite pigment prepared by the above preparation method is a flaky aluminum powder pigment coated with bismuth oxide on the surface, and the pigment is a flaky aluminum powder pigment coated on the surface of bismuth oxide. The emissivity is 0.42-0.44, the thickness of the coating layer is 0.2um-0.6um, the brightness L* value of the pigment is 65-68, and the b* value of the color channel from blue to yellow is +29-+34.

Example 4

(1) Add Bi(NO) _3． 5H ₂ O is as solute, and ethylene glycol is solvent, is mixed with the bismuth nitrate solution that Bi ³⁺ concentration is 0.1mol/L, adds dispersant, aluminum powder wherein, the dispersant that adds in every liter of solvent is 0.5g, so The dispersant is sodium dodecylbenzenesulfonate. The molar ratio of the solute and the aluminum powder is 0.2:1, and after ultrasonic dispersion, the weak base solution with a pH value of 8 is added dropwise at a uniform speed at a rate of 1ml/min to make the Bi in the reaction solution ³⁺ all precipitate; The alkaline solution is ammonia water. The temperature of the reaction system was controlled at 50°C.

(2) Suction filtration after the reaction is completed, the filter residue is dried, and the precursor powder is obtained after grinding;

(3) Put the obtained precursor powder into a muffle furnace for calcination at 500° C. for 2.5 h, and obtain a composite pigment with low infrared emissivity after cooling with the furnace.

The aluminum powder added in the reaction is non-leafing flake aluminum powder with concentrated particle size distribution, and the particle diameter of the non-leafing flake aluminum powder is 40um.

The low infrared emissivity composite pigment prepared by the above preparation method is a flaky aluminum powder pigment coated with bismuth oxide on the surface, and the pigment is a flaky aluminum powder pigment coated on the surface of bismuth oxide. The emissivity is 0.42-0.44, the thickness of the coating layer is 0.2um-0.6um, the brightness L* value of the pigment is 66-68, and the b* value of the color channel from blue to yellow is +12-+14.

The following are the performance parameters of the samples obtained in 4 examples:

Emissivity and chromaticity parameters of the samples in Table 1

It can be seen from the above table that the amount of aluminum powder is closely related to the performance of the composite pigment. In Example 1, the amount of aluminum powder used is relatively high (the molar ratio of solute and aluminum powder is 0.1:1), the coating layer formed by the precursor on the surface of the aluminum flake is thin, and the comprehensive performance of the composite pigment obtained after final calcination is similar to that of pure aluminum powder. Low emissivity and high brightness. In Example 2, the amount of aluminum powder is relatively low (the molar ratio of solute and aluminum powder is 0.4:1). In addition to nucleation on the aluminum sheet, the excessive precursor nucleates and grows outside the aluminum sheet, and forms bismuth oxide particles and inclusions after calcination. Between the aluminum flakes, the composite pigment thus has a lower brightness and a higher infrared emissivity. In example 3, the amount of aluminum powder is 2.7g (that is, the molar ratio of solute and aluminum powder is 0.2:1). At this time, the proportioning ratio of solute and aluminum powder is the best, the thickness of the coating layer formed is moderate, and the coating effect is the best. The bismuth oxide particles mixed outside the aluminum flakes are rare, so the brightness of the composite pigment is the lowest, and the infrared emissivity is small. At this time, the metallic luster on the surface of the pigment is weak, and it has the best stealth performance compatible with visible light and infrared. The molar ratio of solute and aluminum powder in example 4 is the same as that of example 3, all under the optimal ratio, the thickness of the cladding layer is moderate, the metallic luster of the aluminum sheet is covered, and the brightness decreases. As the calcination temperature is adjusted to 500 degrees, the crystal form of bismuth oxide coated on the surface of the aluminum powder changes from β phase to α phase, and the emissivity of α phase bismuth oxide is similar to that of β phase bismuth oxide, but the color is much lighter. The composite pigment of Example 4 also has reduced brightness and emissivity, but the b* value is much lower than that of the composite pigment of Example 4.

It can be seen from Figure 1 and Figure 2 that the composite pigment is essentially composed of aluminum flakes in the inner layer and bismuth oxide in the outer layer. The emissivity increases only slightly across the bismuth oxide layer with little loss. The surface of the composite particles is very rough, which is beneficial to enhance the loss of visible light (0.38um-0.77um) and reduce the brightness of the composite pigment, so that the composite pigment has the stealth performance compatible with visible light and infrared.

It can be seen from Figure 3 that the position of the infrared reflection curve of the composite powder pigment is close to the position of the characteristic curve of the pure aluminum powder pigment, and has excellent infrared reflection performance.

Comparative example

(1) Add Bi(NO) _3． 5H ₂ O is used as a solute, ethylene glycol is a solvent, and Bi ³⁺ concentration is prepared as a bismuth nitrate solution of 0.25mol/L, and a dispersant and aluminum powder are added thereto, and the dispersant added in every liter of solvent is 0.3g, so The dispersant is sodium lauryl sulfate. The molar ratio of the solute and the aluminum powder is 0.2:1, and after the ultrasonic dispersion, the dropping rate of 2ml/min is added dropwise at a constant speed to a weak base solution with a pH value of 8 to make Bi3 ⁺ in the reaction solution all precipitate; the base The neutral solution is ammonia water. The temperature of the reaction system was controlled at 65°C.

(2) Suction filtration after the reaction is completed, the filter residue is dried, and the precursor powder is obtained after grinding;

(3) Put the obtained precursor powder into a muffle furnace for calcination at 400° C. for 2 h, and obtain a low-infrared emissivity composite pigment after cooling with the furnace.

The aluminum powder added in the reaction is non-leafing flake aluminum powder with concentrated particle size distribution, and the particle diameter of the non-leafing flake aluminum powder is 25um.

The low infrared emissivity composite pigment prepared by the above preparation method is a flaky aluminum powder pigment coated with bismuth oxide on the surface, and the pigment is a flaky aluminum powder pigment coated on the surface of bismuth oxide. The emissivity is 0.47-0.49, the coating thickness is 0-0.3um, the brightness L* value of the pigment is 75-79, and the b* value of the color channel from blue to yellow is +33-+38.

Example 5 is a comparative experiment. Although the ratio of solute and aluminum powder is the best, the reaction rate is too fast, and a large amount of bismuth oxide nucleates and grows in the same phase outside the aluminum flakes, and is mixed between the aluminum flakes. The coating effect is extremely poor, and finally The obtained pigment not only has too high emissivity, but also has very high brightness, which makes it difficult to achieve the purpose of making light and infrared compatible stealth.

The above-mentioned embodiments only illustrate the principles and effects of the present invention, but are not intended to limit the present invention. Anyone skilled in the art can modify or change the above-mentioned embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes made by those skilled in the art without departing from the spirit and technical ideas disclosed in the present invention shall still be covered by the claims of the present invention.

Claims (7)

1. A composite pigment with low infrared emissivity, characterized in that: the pigment is a flaky aluminum powder pigment coated with bismuth oxide on the surface, the composite pigment has an infrared emissivity of 0.39 to 0.55 for 8 to 14um, and the coating thickness is 0.2um-0.6um, the brightness L* value of the pigment is 65-77, and the b* value of the color channel from blue to yellow is +2.8-+42. 2. the preparation method of the described low infrared emissivity composite pigment of claim 1 is characterized in that, comprises the steps: (1) Use Bi(NO) _3· 5H ₂ O as the solute and ethylene glycol as the solvent to prepare a bismuth nitrate solution with a Bi ³⁺ concentration of 0.05-0.20 mol/L, and add a dispersant and aluminum powder to it. The dispersant added to the solvent is 0.5-0.7g, the molar ratio of the solute to the aluminum powder is 0.1:1-0.4:1, and the alkaline solution is added dropwise at a uniform speed after ultrasonic dispersion to precipitate all the Bi ³⁺ in the reaction solution ; (2) Suction filtration after the reaction is completed, the filter residue is dried, and the precursor powder is obtained after grinding; (3) Put the obtained precursor powder into a muffle furnace for calcination at 400-500° C. for 2-3 hours, and obtain a low-infrared emissivity composite pigment after cooling with the furnace. 3. The preparation method of the low infrared emissivity composite pigment according to claim 2, characterized in that: the dispersant is sodium dodecylsulfate or sodium dodecylbenzenesulfonate. 4. the preparation method of low infrared emissivity composite pigment according to claim 2 is characterized in that: the aluminum powder added in the reaction is the non-leafing type flake aluminum powder that particle size distribution concentrates, and described non-floating type flake The particle size of aluminum powder is 1-50um. 5. The preparation method of the low-infrared emissivity composite pigment according to claim 2, characterized in that: after ultrasonic dispersion, the weak base solution with a pH value of 8-9 is added dropwise at a uniform speed at a rate of 0.2-1.5 ml/min All the Bi ³⁺ in the reaction solution was precipitated. 6. The preparation method of the low infrared emissivity composite pigment according to claim 2, characterized in that: the alkaline solution is ammonia water or sodium hydroxide solution. 7. The preparation method of the low-infrared emissivity composite pigment according to claim 2, characterized in that: in the step (1), the constant temperature of the reaction system is controlled at 30-60 degrees.